FWIW… On MacOS, today, when time was pressing (of course!!!), my Ruby had somehow updated itself to vs 3.3.0, and even with latest Jekyll I had indecipherable 
errors. No double install of Ruby, ruby doctor found nothing, no other solution found by me… I noticed in the errors rubylib (or so) at version 3.2.x. So I went the trivial way: I just trashed the entire $HOME/gems/ folder.
Ran “update everything”, which recreates the bespoke gems folder (takes a while), and lo and behold, all fine now, no errors on bundle install / bundle update! May it help someone else…
[How can I flag this as “solution”?]
maybe there has to be a reply in order to have a solution?
Thank you, Ron :). Had I written this in 2 separate posts…