Back when I started riding MTBs they were mostly rigid by default and it wasn’t really a problem TBH…
I have had a fully rigid SS bike in recent years, but not as my only MTB, and it has since been disassembled…
Weirdly in my head I had sort of put rigid and singlespeed together almost by default, But I am currently assembling a geared, rigid MTB (will probably end up with with panniers and maybe guards) mostly from my spares bin, as a sort of utility/commuter/touring MTB. Really just to see if it gets much use…
Why not go rigid though, if it suits your expected riding and the simplicity appeals? There’s plenty of kit about still and most importantly (IMO) a nice wide tubeless front tyre makes a rigid bike much more comfortable offroad than some would have you believe…