When I travel to a new country, I always try to get a photo of a flag and/or video of it flying in the breeze. I enjoy trying to remember the flags of the places I've been (and not been).
I found this website: https://shaheeilyas.com/flags/ and tried to quiz myself. This is really hard, but I did get a few of them.
If you prefer identifying the actual flags, try this: https://www.jetpunk.com/quizzes/flags-of-the-world-quiz
And if you prefer multiple choice, https://world-geography-games.com/en/flags_world.html. (With this one, you can limit it to just Europe (or any other continent.)
Sorry, but I'm a bit of a trivia buff, so I enjoy these kinds of quizzes. Is anyone else a flag aficionado?