I know you are all super excited for Bartender on Big Sur (I have been getting all the emails 😂).
As you already know the changes in Big Sur are massive, because of this Bartender needed a complete internal rewrite to get it working on the new macOS beta.
Bartender 4 for Big Sur is coming along well, and testing is progressing, as you can imagine this is a big update and as such it is taking a while to get it ready for public testing.
I will release a beta test build as soon as its ready, and fully tested here. Its just not quite ready yet.