Catacombs in Rome

To the best of my knowledge they all require a guide. They don't want you getting lost underground. You don't need to lock in a time. Just show up and take the next available tour in English. Our experience was that the tours were very frequent.

Someone had asked a couple of weeks ago whether you enter then Capuchin Crypt unescorted/alone to which I had answered that you do.

Maybe that’s what you remembered?

https://community.ricksteves.com/travel-forum/italy/capuchin-crypt-in-rome-3e5b5bd9-efc4-45d0-aeb3-b66478318132

Here's the thread referred to above.

I was finally able to get the Borghese tickets for 11am-1p. Thinking we will do the Capuchin Crypt the same day.

Have a great trip!

You don't need to lock in a time. Just show up and take the next
available tour in English.

That was our experience with San Sebastiano. We just walked in and signed up for the next English tour. I don't remember how long we had to wait until it got going, though. It works that way for St. Callixtus, and I believe for Domitilla and Priscilla as well.

https://www.catacombe.roma.it/en/index.php

http://www.catacombe.org/uk_index.html

http://www.domitilla.info/idx.htm?var1=docs/en01.htm

http://www.catacombepriscilla.com/index_en.html

I don't personally consider the Capuchin Crypt a catacomb in the sense of the really old (from 2nd century) subterranean "tufa tunnel" cemeteries which were outside the city walls, as was the custom. That doesn't mean it's not interesting! It just doesn't exhibit the valuable frescoes/iconography or burial customs of the much more ancient eras.

You would not see any bones: those which would have been visible in opened/deteriorating tombs have been relocated out of respect for the deceased. Respectful visitor attire is requested for these religious sites.

We did San Sebastion two weeks ago. I'd recommend another one. The guide walked us through the catacombs so quickly we could not stop for even a second to view them properly and enjoy the experience of seeing them.

I think individual experience regarding the guides depends on which one you end up with.
Results may vary.