I have a Librem 13 and have installed Debian 12 on it, which works fine except that the keyboard settings are not right, for example the key for | which is in an unusual place on the Librem 13 keyboard, that key does not work for me in Debian.
How to get the right keyboard settings for Librem 13 in Debian?
Try Settings → Keyboard → Input Sources, then change to a different keyboard layout.
There is a list there, with many different layouts for different languages, the one I have selected is “English (US)” which works almost okay but the “|” key and perhaps some others are wrong. I don’t think any of the options shown in the list would work, because the L13 keyboard has a specific layout that Purism has come up with, which I guess is not available in Debian by default. I’m wondering if the L13 keyboard layout could be installed somehow, so that a new entry like “Purism L13 keyboard” would show up in the list. I imagine there might be a file somewhere in the PureOS repositories, a file specifying the keyboard layout, and then that file could be copied into the right place. Or maybe it could be installed via a .deb file. But I don’t know if it really works like that, just guessing and hoping someone who knows more can explain how it works. 
There is plenty of discussion in this forum regarding messing around with keyboard mapping. However it has always been opaque to me how this all hangs together, hence I can’t answer the question.
(For example, if you are making it work by configuring at the graphical level, it might fail to work for the rare occasions when the GUI doesn’t come up and you login locally using the login prompt - which might be just when you really really want a working “|” key. Can the key be made to work in all scenarios? i.e. at the lowest possible level?)
If it were me, I would probably Live Boot PureOS and then look around for how PureOS is making it work, assuming that that is indeed the case.