I’m not a filter expert, but having tried to learn them lately I think the Filters article is aimed at command line and special cases, while the GUI’s Creating a new backup job is too vague on translations intended to help. For example, I think the intent there is you type in a folder, and the GUI adds * wildcards and a trailing slash. You can see what it made using the three-dot menu, and you might also notice some bugs where GUI may need to be told a few times (via dropdown) what you want it to do. Keep at it. You can look in Commandline to see what sort of --exclude the GUI built. I think yours looks right for that setting, but not for input to GUI…
Problems using test-filter gets in some of this, while also giving ways for you to test filters, without backup.