How to Reinstall the macOS Anew - No TMB Prior to Upgrade

Reinstalling the macOS:

macOS X Catalina 10.15 is 64Bit only, and, with the being the case, upgrading to it would result in your 32bit apps being inaccessible after the upgrade. If you're installation is having issues, then you can always install the macOS anew.

The Scenario: Having upgraded to macOS X Catalina10.15. You realize that you need to downgrade in order to run older, 32bit-installed apps, yet you never made a Time Machine Backup, prior to the upgrade. You have no access to the internet at the moment.

To Fix This: You would reinstall the macOS anew to pre-Catalina:

A. Create a Time Machine First (If an applicable option):

Create a Time Machine Backup of your Mac, that way you can have something to restore your Mac from, should anything go wrong with the reinstall, and need to migrate it all back. Use an External Hard Drive at least 1.5 times the size of the Internal Hard Drive. Take a photo of the app you have installed.

B. Then... Reinstall the Mac OS that was Previously Installed...

I. Create a USB Bootable Installer:

1. Go Here: How to Create a Bootable Installer for macOS - Apple Support
2. Use a Separate Mac: to create this for the macOS version install you need to downgrade to.

II. Erase the Hard Drive:

1. Boot: into Recovery Mode: Hold Down [Command + R] upon boot
2. Select: Disk Utility
3. Erase: the all partitions

III. Boot From USB Bootable Installer:

1. Plug in: The USB Bootable Installer
2. Hold Down: Option upon to boot into Startup Manager
3. Select: the USB Bootable Installer for the Startup Drive
4. Proceed: from there as necessary with the Install

C. Once the macOS is Installed - Reinstall the Apps...

I. Create a Second Time Machine First:

With a new clean install, create a Time Machine Backup of your Mac.

II. Use Migration Assistant:

1. Go Here: How to move your content to a new Mac - Apple Support
2. Scroll to: Use Migration Assistant
3. Proceed from there as necessary

III. Update Manually:

1. Contact: the Developer for the license, informing them of a failed install
2. Update: the installed software to 64bit (except for the macOS to upgrade)
3. Proceed from there as necessary

IV. Create a Third Time Machine:

With a final install of updated apps, create a Time Machine Backup of your Mac.

D. Upgrade to Catalina, now that 64Bit Software is Installed