Support & EOL for 3.5.17

Yes, I’d definitely recommend upgrading. There have been any number of improvements, including PHP 7.4 support. It’s also just so much easier to upgrade if you stay on top of it.

I’d say most add-ons don’t have to be upgraded going from v3-v5, though of course, you’ll want to check and make certain you have the newest version and that there is no indication it’s not v4 compatible. If it works on v4, 99% of the time it will work on v5.