Red screen with big "T" possible fix?

Many of my third party text plugins are showing the red screen since I updated to FCPX 10.5. I'm still on Catalina 10.15.7 and wondering if that's the reason?
So far what I found online for the possible reasons for this particular red screen is:
1. the latest FCPX is needed
2. must be logged into the same Apple apps account that FCPX was originally purchased from.
3. need to update to the latest OS

If this is true, that I need Big Sur, can I fall back to the previous FCPX? Thoughts?

1. You have the latest version of FCP (no longer X)

2 and 3 are just plain wrong.

Third party plugins need to be updated for the new version of the application. You might try reinstalling them, but you should also contact the developers for updates. 

Thanks Tom! Very helpful. I'm still learning FCPX since switching back recently. Such fun, but so much to learn.

Disable any automatic update from your Mac. (i guess it is already done).

- wait several months before updating any new OS anyway.

- update OS and Fcp (any update) only when you have checked that all your third-party plugins are good to go on every dev. site.

Thanks Stu, appreciate the reminder!

I updated FxFactory and plugins I have downloaded through them all work. Now I'll need to contact the other vendors.