tl;dr: The Subject line may tell you all you need to know.
I do not read all the Mac sites, so if this has been reported elsewhere, it slipped under my RADAR.
At some point in the later history of macOS, optical disc burning capability was removed from Disk Utility and moved to Finder, either via the File menu or contextual menu. The move may have stumped a few users for awhile, but it’s easy to get used to. Since then, I have burned countless DVD and Blu-Ray videos with very little trouble. Physical media is NOT dead.
When macOS Catalina 10.15 was released in the fall of 2019, it should have been reasonable to assume that disc burning was still supported, so when I was greeted with an erroneous error message when attempting to burn .iso or .toast images, I filed a bug report with Apple. It was still possible to burn images to disk with the hdiutil command in Terminal, so disaster averted.
A few iterations of Catalina and a few bug reports later, it became possible to burn .iso images to DVD, but attempting to burn .toast images to DVD, or ANYTHING to Blu-Ray, except through hdiutil, was still impossible. At this point I started to assume that there was no reason why Apple should support .toast images, and that Blu-Ray was a “bag of hurt” that could be dispensed with.
Some time after macOS Catalina 10.15.5 and its supplemental update was released, I needed to burn a Blu-Ray image to disc, and through force of habit, I decided to give disc image burning through Finder one more last try. AND IT WORKED! It would appear that the disc burning capability that existed in Mojave and previous versions of macOS has been completely restored. That means it is finally possible to burn .iso and .toast disc images to DVD and Blu-Ray.
And here’s the helpful feedback I got when I posted this to the Usenet group comp.sys.mac.system:
media is NOT dead.
yes it is.
No it absolutely isn’t.
Yes, it definitely is.