Wildgoose, back in the 1990's I first used a computer (yeah, an Apple macintosh, Performa) -- in order to understand the ins-and-outs of working with computers, David Pogue was my mentor (through his book, Macs for Dummies).
One thing that would crop up from time to time was a fatal (BOMB!) error, and Pogue described this as being likely caused by corrupted font suitcases. Solution? -- try https://www.macissues.com/2014/04/18/how-to-troubleshoot-font-problems-in-os-x
(I have seen some reports online of the default font San Francisco being the root cause, for some arcane technical reason).