There are a lot of differences and a lot of similarities between the operating systems here. It will take you time to get used to no matter what you do. Start by swapping your apps on your existing Mac, trade out any apps that you know won't work on Linux with apps that do. That way, you spend some time in your existing environment with the new apps you're going to need going forward.

Next, make sure to test out your peripherals in a live environment. Does everything you use with your computer work correctly? If not, find out why. See if you can mitigate it, or if you'll need to replace stuff.

Finally, be willing to experiment. I know others in this thread will recommend various desktop environments and distributions to you. Try many of them. GNOME is good and simple out of the box, feels kinda mac-like, but if you want to completely replicate the functionality of macOS, KDE Plasma has more options for that like global menus and the file management app (Dolphin) is incredibly extensible and customizable.

Try to have fun with it, and don't give up. It takes time to learn a new way of working, and you will likely have frustrations along the way, but ultimately the goal is to learn and figure out what works best for your needs.