I have an intel iMac. Should I update to Somona

Yes. Macs whose hardware model year is 2019 or later will run Sonoma, whether they are Intel-based or Apple-Silicon-based Macs.

Some features might be Apple-Silicon-only, like the ability to use the Touch ID keyboard, or to run iPhone / iPad apps whose developers allow them to be made available through the Mac App Store.

BiffoBails wrote:

Will an 2019 iMac running on Intel chip support sonoma

ref: macOS Sonoma is compatible with these computers

It sure makes moving forward more seamless.

It never pays to get behind in the software or hardware.

stay current, bug fixes, security patches

Keep your Mac up to date

If you value your user data

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.

More than one device, more than one backup methodology.

Servant of Cats wrote:

• The OP's tag line says they have a 21.5' iMac.

If they have a 1 TB HDD, that will be a slow 5400 rpm notebook HDD.

• If they have a 1 TB Fusion Drive, that will be a slow 5400 rpm notebook HDD paired with a stingy 32 GB of flash (SSD) space. (The original 1 TB Fusion Drives included 128 GB of flash (SSD) space.)

These iMacs are designed in a way that makes performing internal upgrades difficult / risky (for individuals) – and expensive (when done by a repair shop).

A better option might be to get an external SSD and put the startup volume on it. 2019 iMacs have USB-A (USB 3) ports and USB-C (Thunderbolt 3) ports, which means they're compatible with a very wide range of external SSDs.

On may of your points I agree with the options you have presented though

The Object of my earlier posting to OP was a cautionary if they have High Expectations for Performance under the present configuration

As we both know, the by-line associated with many users posting are not always the same computer in question

I post elsewhere and my by-line shows a device I not longer own

Let us not open an Off Topic about this matter 😎

FYI to Apple Specification based upon the 21.5 2019 iMac

iMac (Retina 4K, 21.5-inch, 2019) - Technical Specifications (CA)

Storage1

• 3.6GHz
• 256GB SSD
• Configurable to 1TB Fusion Drive
• 3.0GHz
• 256GB SSD
• Configurable to 1TB Fusion Drive

The OP's tag line says they have a 21.5' iMac.

• If they have a 1 TB HDD, that will be a slow 5400 rpm notebook HDD.
• If they have a 1 TB Fusion Drive, that will be a slow 5400 rpm notebook HDD paired with a stingy 32 GB of flash (SSD) space. (The original 1 TB Fusion Drives included 128 GB of flash (SSD) space.)

These iMacs are designed in a way that makes performing internal upgrades difficult / risky (for individuals) – and expensive (when done by a repair shop).

A better option might be to get an external SSD and put the startup volume on it. 2019 iMacs have USB-A (USB 3) ports and USB-C (Thunderbolt 3) ports, which means they're compatible with a very wide range of external SSDs.

As others have suggested

Important is the Hardware on the machine.

Specifically if the configuration is a Fusion Drive or a Rotational / Traditional Spinner Drive.

It will function but the Performance will take a Big Hit

Fusion Drives are a mix of a SSD combined with a Rotational Drive and presented to the user as a Single Drive

The Rotational drive, even the fastest 7200 RPM drive will never attain the same Performance Levels as an All SSD configuration

Be prepared for these possibilities

If one checks the specification from Apple on IMac from 2019 most of those machines have Fusion Drives