I did give the game (from Macintoshgarden) a short try and did not see any error 21 so far.
Host was 10.14.6, guest MacOS 8.6.
As the mouse is practically unusable for the game in SheepShaver, I would use Qemu (Screamer Build) instead.
The mouse looks good in Qemu to me, video is looking better either methinks.
Cat_7 has some builds ready with Screamer sound support.
If need should be, I could upload the package which is working on my side.
Still have a Sierra host OS to try, if that helps, but no HS atm.