how can I downgrade my Mac from macOS Catalina to Mojave ?

Those programs may be 32-bit and need be upgraded to 64-bit, check with the developers for upgrades.

If you still want to downgrade, you can revert from your Time Machine backup:

Restore your Mac from a backup - Apple Support

If you have no TM backup then you'll need to erase your disk and re-install:

How to reinstall macOS from macOS Recovery - Apple Support

All 32-bit programs will not run in Catalina. Been two years of precautionary publicity about that. Have you checked with those vendor's about 64-bit application availability and compatibility with Catalina?

If you performed one last Time Machine backup of Mojave before you upgraded to Catalina, and if you did not reuse that Mojave Time Machine drive for Catalina Time Machine backups — then you should be able to boot into Recovery and select Restore from Time Machine backup. That will wipe your boot drive, and restore your Mac to Mojave just as it was prior to the upgrade to Catalina. Clearly I have not done this, so there may be some APFS issues between Catalina and Mojave. Don't know.

Without a Mojave Time Machine backup, you will lose everything on the current Catalina drive as it must be erased to retreat to Mojave, which now you would need on a bootable USB stick.