Yikes. Guessed as much. Thanks for your explanation.

As for oooold devices - doesn't LetsEncrypt demand key lengths and hash algorithms nowadays that simply weren't implemented back then?

Yes, I guess 2000 would actually be an exaggeration these days, as you can't use SHA-1 or 1024-bit RSA subject keys. So you could maintain compatibility with oold devices, but not with oooold devices.