Multiple OSs on network

[dazzer21-2]

I posted elsewhere that I was getting really poor performance having installed an M1 Mini on my home network, especially as it ran as as smooth as butter beforehand. It's just crossed my mind that potentially this could be an OS issue. Because I want to be able to use 32-bit apps, my iMac is on the most recent version of Mojave. The Mini is on Big Sur. Are there any known incompatibility issues? And would it be an OS or M1 problem? TIA.