How do I uninstall Catalina? I can't use my MacBook Air for anything anymore.

If you performed a Time Machine backup before upgrading to Catalina, then you have a means to revert to the previous operating system as it was before you upgraded to Catalina. You would boot into Recovery mode, and select Restore from Time Machine Backup. If you did not perform a Time Machine backup prior to the Catalina upgrade, then you are faced with a clean install from a bootable USB stick, and loss of any existing data on Catalina.

Do not attempt to perform that boot into Recovery and Restore from a Time Machine backup if you do not know what is on that Time Machine backup, or when it was done. You could be setting yourself up for substantial data loss in that gap before you performed the Catalina upgrade. The best time to perform a Time Machine backup is immediately before the upgrade, so there is no doubt what is on the drive. Any new documents that you have created on Catalina should go on a USB stick for now, or start performing Time Machine backups from Catalina.

If you do not want to pay for a Microsoft Office 365 subscription, you could install the free, 64-bit LibreOffice Suite on Catalina. This is an MS Office clone that is frequently updated, and has the best Office document support next to Microsoft applications.

The use of LibreOffice, or Google Docs is solely your choice. Although LibreOffice will switch to a donation page prior to download, those donations are purely optional. I use LibreOffice because I have no assurance that documents stored on a Google cloud service are not mined by Google for information.

I can do it with a backup from my time capsule, otherwise others with need to help

[removed ... /viking]