Hello everyone, I am a Super Mod for the game Rider (Mobile) along with another Super Mod that has been inactive for a while now and not answering my private messages.
Since I don't have that kind of power, I was wondering if there was a way or any procedure to kindly remove him from the moderation team with his agreement (if he ever answers) so that I could add other people to help me with moderation while keeping the team fresh and active!

Thank you for your help, have a nice day.

I’d suggest you ask for this in this Forum Thread so a Site Mod can remove him.
https://www.speedrun.com/the_site/thread/dueac

I was considering posting my request over there but I was afraid it would be off-topic! Thanks for the advice though, I'll head off there if this thread doesn't find its target

This thread isn’t going to get you anywhere. You need to post on the one linked above, as that one is specifically created to deal with situations like this. You can, per the first post:

Request the removal of inactive Super Moderators.