Looking at the numerous bug reports I get the impression that the new bootstrap code possibly in some cases might order CAM devices incorrectly, maybe due to some confusion/bug in hardware recognition, and in this case booting fails.
It might also be an issue with particular optical drives, as I some time ago had to try multiple DVD drives from my storage until booting the ISO succeeded. (I suspected some problem with the drives, as they were used but refurbished. But, further examination of the drives 'rejected' by FreeBSD DVD only showed perfect functional state, not downgraded in any way.)
There are several reports in the PR linked in your link that look like as if unplugging the optical drive and installing via USB stick could be a work-around to make FreeBSD work.
In this case, instead of an internal optical drive, one probably would need an external one that can be unplugged while booting.
Another alternative might be installing a switch on the front plate, so you can power on the internal optical drive after boot-up.
Sadly, both options are not viable for me.
It might also be an issue with particular optical drives, as I some time ago had to try multiple DVD drives from my storage until booting the ISO succeeded. (I suspected some problem with the drives, as they were used but refurbished. But, further examination of the drives 'rejected' by FreeBSD DVD only showed perfect functional state, not downgraded in any way.)
There are several reports in the PR linked in your link that look like as if unplugging the optical drive and installing via USB stick could be a work-around to make FreeBSD work.
In this case, instead of an internal optical drive, one probably would need an external one that can be unplugged while booting.
Another alternative might be installing a switch on the front plate, so you can power on the internal optical drive after boot-up.
Sadly, both options are not viable for me.