Okay, I ACTUALLY MANAGED TO BURN A DISC IMAGE yesterday, with the transitions and everything. Mind you I had to start from scratch, as I had given up on opening the .disc file from 19.2. I saved and resaved....and then at some point Toast just decides to stop saving. I had to "Save As" and replace the file from then on. At one point I went to another program to check something and I got the spinning beach ball in Toast! But I had other things to do, so I just walked away. When I came back (10? 15? mins later) it was back to normal, so...I dunno. I got it to do what I wanted. BUT IT SHOULDN'T BE THIS HARD.
(Side question: Big Sur peeps, are you finding that Mac is just slow at some things like serious lags between hitting save and getting the save dialog window?)
I have *not* tried the "erase everything, install 19.3" trick. Maybe I should. Again, THIS SHOULDN'T BE THIS HARD.