Thanks. If you have any clue on how it could be resolved, please take part in remedying.
.
As far as I can tell, I did not use BURG in any way. I did not try to replace GRUB or to add kernels or such. I did not even try to customise GRUB, I only wanted to have a tool at hand for repairing eventual boot failures.
In the PC session leading to EOS’s boot failure, I did not do anything prior to or after yay system update. yay was really the breakpoint here, whatever the deeper, maybe longstanding root of the problem might be.
.
Even if so, that is not @mjl’s question. @mjl just wants to know whether and which precautionary measures should be taken – really aside from question of fault. I only wanted to contribute to the former topic.