For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
As often as you need a bugfix or a new features provided in GitHubUpdate from GitHub
Only if you want to install a new plugin.Go to Extensions > Extension Manager > Discover
Click 'Purge Cache' and then 'Discover'
Select your plugins and click 'Install'
Go to Extensions > Plug-in Manager
Enable your plugins
And whenever something isn't working correctly on your site, I've learned to NEVER post on the forum until you update from github first. It's fixed 50% of my issues. Hahaha.
PS - You post A LOT. Holy CRAP!!!!! (And I'm saying that in a nice calm voice, but rolling my eyes slightly).