I upgraded from Jenkins 2.263.4 to 2.277.1 and I upgraded all installed plugins.
Jenkins pretty much stopped working after that. I could not edit my jobs, it wouldn't save, the screen output was garbled, it was a mess. Release notes for 2.277.1 indicate that it had a major UI change and plugins that weren't updated might not work.
So I fell back to 2.263.4. And then I was presented with a bunch of plugin dependency errors (as expected). However, there is no obvious way for how to downgrade those plugins.
If we go to the Plugin Manager -> Installed page it just says "Failed to load......" and there is no option to "Downgrade". Funny enough, all the plugins that successfully loaded had a downgrade option, it's the failed to load ones that did not.