2018 Mac Mini, latest version of Catalina, runs like greased lightning over here. Not sure why Renoise is running poorly for you. I don’t use any plugins or sound generators outside of what Renoise has built in or has been coded in Lua for Renoise. Not knowing whether you do or do not use plugins (assuming you might?) maybe there is an issue with a particular plugin?
Wish it worked for you - have you tried installing earlier Renoise versions- some people have success that way.