All is done and everything went perfectly that time, I appreciate it man. I'm thinking I wasn't properly updated before. either way Hell Yea!!Not knowing how you got out of your bootloop or what caused your bootloop in the first place, in my opinion it would be a good idea to either factory reset or fastboot flash the latest factory image so you can start fresh (back up any files you need to save first). After doing that you shouldn't have to specify which slot, it should flash the patched boot image to the slot you are on automatically.
Since the Beta Magisk was updated yesterday to 21.2 make sure you when you enter the command "fastboot flash boot <name> that you use the name of the patched boot image. When I updated yesterday the name of the patched boot image found in the downloads folder after patching changed from "magisk_patched.img" to "magisk_patched_aE2Jx.img". So double check to make sure you use the actual name of whatever you ended up with. Not sure if this was this case for others who updated.
So for instance, yesterday I had to use the command "fastboot flash boot magisk_patched_aE2Jx.img" (without the quotes).
EDIT: Apparently their was a commit added to Beta 21.2 where the name of the patched boot image will change every time you patch your stock boot image.