How to downgrade macOS from Tahoe to Sequoia?

Jason—_ wrote:

my issues are storage due to macos taking around nearly 50gb of 128gb storage

Downgrading the OS is not the fix for a Mac with limited storage, and 50 GB is not a lot of system data, as storage goes.

Your biggest problem is the lack of storage capacity built into your MacBook with the 128GB drive. There is no fixing that, but you might use a portable external drive to house some of your folders and documents. The only real long-term fix is to replace the computer with one that has much more capacity.

The category named System Data (or Other) is a general category that measures the storage space used by all Apple and third-party files that don’t belong to any more specific category like Applications, Documents, Messages, Music Creation, Podcasts, Trash, and TV.

You can’t directly manage the contents of system data. That is done by macOS. The category varies in size depending on the current state of your Mac.

What you can do to create more free space:

• Reboot your Mac at least weekly. Let the OS clear caches and do housekeeping.

• Empty the Trash in the Dock. 

• Empty the trash in the Photos app.

• Delete unused and unneeded application installers from your downloads folder and desktop. No need to store on your Mac what you can freely download any time.

• Transfer files that you don’t use daily to an external drive and then delete them from the startup drive and empty the trash. Files that take up the most room are movies, images and music.

This from Apple on the subject of freeing up space:

Free up storage space on Mac - Apple Support

Jason—_ wrote:

my issues are storage due to macos taking around nearly 50gb of 128gb storage

Stop there ! !

There are no 13 inch MacBook Air computers that Qualify to Run and install macOS 26 Tahoe that come with a 128 GB Capacity Internal Drive

Some of the below computers may have a 256 GB Capacity Drive or if custom ordered a much larger Internal Drive

• MacBook Air (15-inch, M4, 2025)
• MacBook Air (13-inch, M4, 2025)
• MacBook Air (15-inch, M3, 2024)
• MacBook Air (13-inch, M3, 2024)
• MacBook Air (15-inch, M2, 2023)
• MacBook Air (M2, 2022)
• MacBook Air (M1, 2020)

Downgrading to an earlier macOS version is not a task to be taken lightly. It's easier and wiser to work through any problems you are experiencing than trying to downgrade macOS.

Before you attempt to downgrade your Mac, you must first cross your fingers, kiss the St. Christopher and hope all goes well on your journey.

Downgrading requires that you format the drive to erase all the data on the Mac, reinstall the older OS and finally restore your files from a backup. Additionally, the Mac’s firmware may also have been updated when the newer OS was installed, potentially requiring you to use another Mac connected to yours to revive or restore your Mac in DFU mode..  

If that sounds complicated and risky, then you understand the reality.

1) Backup your files to an external disk with  Carbon Copy Cloner  or  SuperDuper! 

2) Download the older macOS version and create a bootable USB installer for it on a USB flash drive. This is insurance in case the Mac can’t/won’t boot in recovery mode. Test that the installer is bootable before proceeding.

3) Start up your Mac in macOS recovery mode. 

a) Launch Disk Utility and format the internal drive. Select the GUID partition scheme, the APFS format and name the drive “Macintosh HD”.  This step will erase all of your stored data from the drive. Quit Disk Utility.

b) Launch Reinstall macOS… and follow the prompts to select the destination drive - Macintosh HD - and begin the reinstall process. Reinstall macOS  

c) If Reinstall macOS… doesn’t offer the OS you want, you can now use the bootable USB installer that you created.

4) Restore items backed up with Time Machine on your Mac from the TM backup made before your upgrade to Tahoe, or restore your files from the CCC or SuperDuper! backup you made before you started the downgrade.

HINT - It's easier and wiser to work through any problems you are experiencing than trying to downgrade macOS.

Jason—_ wrote:

my issues are storage due to macos taking around nearly 50gb of 128gb storage

As far as I know there is no macOS device that ships with only 128GB of storage. 256GB is the minimum. So what device are you are using? Are you sure it’s a Mac?

den.thed wrote:

Excellent job explaining the down-sides of attempting to downgrade the macOS. 👍

Thanks.

Admittedly I have 'adapted' some guidance from others here in the Community in formulating my response. 😉

lkrupp wrote:

Jason—_ wrote:

my issues are storage due to macos taking around nearly 50gb of 128gb storage

As far as I know there is no macOS device that ships with only 128GB of storage. 256GB is the minimum. So what device are you are using? Are you sure it’s a Mac?

According to the Mactracker app, the 13-inch 2020 M1 MacBook Air shipped a couple configurations with only 128GB of storage, unfortunately.

An excellent external SSD for portable computers is the OWC Envoy Pro Mini:

It's available in sizes up to 2 TB.

However, if budget is a concern a possible solution is this configuration:

I have several of them and am very satisfied with their performance.

Jason—_ wrote:

I have an m1 MacBook Air if your confused

In Case you missed the previous posting here it is again

MacBook Air (M1, 2020) - Technical Specifications

Storage2

• ➡️ 256GB SSD ⬅️
  • Configurable to 512GB SSD, 1TB, or 2TB

So stop this nuance regarding " 50gb of 128gb storage "

There are Apple Intel MBAs that came with 128 GB Drive Capacities

But they do not Qualify for Tahoe macOS 26

Right and thank you

🦉-53

Regardless, OP has the tinniest of tiny drives that, IMHO, could /would run into the every " Watching over their Shoulder " for Free Disk Space, be it Sequoia, Sonoma etc.

They might be better off Moth-Balling the existing machine and get something will more Unified RAM and a decent Capacity Internal Drive

To illustrate the earlier point I made to my colleague @stedman 1

Why it was suggested to purchase a newer computer with more Unified RAM and Larger Capacity SSD Drive

1 - In practice, after formatting a 128 GB SSD as APFS / GUID on macOS, you’ll typically see:

about ≈121 GB to 123 GB available

That small range depends on macOS version and how Disk Utility reports space, but anything in that window is totally normal.

2 - Typical numbers you’ll see

Usable after format: ~121–123 GB

macOS 15 Sequoia install size: ~18–22 GB

• (system files + preinstalled apps + APFS system volumes)

Free space remaining

About 98–103 GB available

Can the computer withstand having between 98 GB to 103 GB of Usage Space ?

3 - These figure to not account for installing an Apple Add-on Applications, Third Party Applications. Personal files like Music, Pics, Videos and other types of personal files  

Only the recipient could answer that question

Owl-53 wrote:

MacBook Air (M1, 2020) - Technical Specifications

Storage2

• 256GB SSD

• Configurable to 512GB SSD, 1TB, or 2TB

According to the folks at EveryMac.com, there was an education-only option that could be configured with just 128 GB of internal storage:

https://everymac.com/systems/apple/macbook-air/specs/macbook-air-m1-8-core-7-core-gpu-13-retina-display-2020-specs.html

D.I. Johnson wrote:

Owl-53 wrote:

MacBook Air (M1, 2020) - Technical Specifications

Storage2

• 256GB SSD

• Configurable to 512GB SSD, 1TB, or 2TB

According to the folks at EveryMac.com, there was an education-only option that could be configured with just 128 GB of internal storage:

https://everymac.com/systems/apple/macbook-air/specs/macbook-air-m1-8-core-7-core-gpu-13-retina-display-2020-specs.html

https://discussions.apple.com/content/attachment/75edc236-270c-4cea-a861-324281739bb8

Right and thanks 🦉-53

Though, to be forwards about the issue

The major bottleneck, as I see it, is the combo of 8 GB Unifies RAM and a 128 GB SSD Drive

Whether OP stays with Tahoe or downgrades back to Sequoia or Sonoma.

The exact same Lack of Storage Space is going to rear its ugly head again and again etc

One gets exactly what they were given or purchased as None of those components can be UpGraded - Soldered to the Logicboard - Full Stop

Excellent job explaining the down-sides of attempting to downgrade the macOS. 👍