Do you mean you reinstalled Windows? If you didn't backup your TB data, did the reinstall backup the AppData folder in a windows.old folder? The TB profile folder is located in ...\AppData\Roaming\Thunderbird\Profiles\<8charstring>.default. You can replace the new Thunderbird folder with the backed up Thunderbird folder, or copy the msgFilterRules.dat files, but the folders have to be recreated if they aren't in the new setup.

Thanks for responding. My computer was in repair and I didn't have a chance to back up my folders. Since the tech installed the new version of Windows 10, there was no backup. I found the msgFilterRules.dat file, but unfortunately I think I have to just recreate all of my filters. I appreciate you assistance in helping me figure this out. If there is anything else you may think of that I could do, that would be great. Have a great day.

The only other thing I would add is to encourage you to make regular backups of the Thunderbird folder:

C:\Users\<winusername>\AppData\Roaming\Thunderbird

Restoring it is as simple as replacing the existing folder with the backup, and this works also for copying a TB setup to another computer.

Thanks. I'm not that savvy. Just save to a flash drive?

Yes, save to a flash drive, external hard drive, different partition or cloud storage, depending on the size. To save space, right-click the Thunderbird folder, Add to zip archive (or similar). Compact folders and close TB before making the copy.

Thank you so so much for helping me with this. Really appreciate it.