The time signatures by themselves would not be polyrhythms. we have to combine the signatures to get polyrhythms. Again we to look to jazz – two or more meters:https://www.moderndrummer.com/article/january-1978-jazz-drummers-workshop-polyrhythms/
3/4 in and of itself is considered simple time as is 2/4 and 4/4
As far as playing polyrhythms on guitar, bass, keyboard, and this is related to a post I edited in this thread - my last post in the thread that simply says, “edit… etc,” and it is basically a deleted post:https://forum.renoise.com/t/how-african-polyrhythms-are-the-root-of-european-club-music/49150
Polyrhythm is really something that exists in the lands of drums and percussion - obviously, rhythm instruments. While rhythm is a big part of playing guitar I think it would be a little difficult to play two rhythms on guitar simultaneously without 3 hands.
A drummer in a rock band has two hands, and two feet. Allowing for example: a 4/4 to be played on the kick, a 6/4 on the pedal of a hat, and two hands you could theoretically play 3/4 on the snare, and hit your toms in 12/4
Now you can begin to layer the instruments over that in different time signatures if you want, but at some point you loose groove. So if the guitarist comes in with a rhythm in a completely different time, and the bassist, and the keyboardist. You have, “experimental music,” that may not groove.
Groove, and whether something is in the pocket are also things to consider with music, and polyrhythm.