The strumming guide is a great start for learning some different common strums. In my experience, you can play a song with any strum pattern (as long as it is in the right time) and it will sound okay. You can play any some just as down down down down…it just isn’t as satisfying. As I learned more strum patterns, I realized that once I learned a pattern well enough to consistently keep it to that 4/4 time, it would fit into any song…it just might not sound like what the artist performed. I’ve found that when I don’t know what strum to use, starting with down up down up down up down up (four total beats) is a good first choice and usually works for any song even if it doesn’t sound like what the artist does. When I am learning harder songs, I start with down down down down since it gives me more time to do the chord changes. The trick is to give each line of the song (usually each chord) the same number of beats — you want to keep doing the full strum pattern each time, not cutting it short to “fit in” a chord (sometimes the chords aren’t in exactly the right place relative to the lyrics…trust your strum!).
My favorite strum is down down up up down up (note that there is a missing down beat which gives this strum a bouncier feel). It took me a really long time to learn this strum well enough that I could actually play it at the proper tempo, consistently, while singing, and also changing chords correctly. This strum works really well for folksey songs, such as Someone to Lava: https://ukutabs.com/m/misc-cartoons/someone-to-lava/
For songs with 3/3 time, I like to do down up down. This works really well for rainbow connection: https://ukutabs.com/t/the-muppets/rainbow-connection/.
One last thing that was not very fun but did help me was to practice my strumming using a metronome. My goal was to become more consistent and play the same number of beats for ever 4 beat measure. I liked this visual metronome: https://www.youtube.com/watch?v=y_QqlHxMGnc&t=107s
I hope that this was helpful. Enjoy learning to strum you ukulele!