We can’t really help you with a procedure that we can’t see. As far as I can tell, you have not posted the link. So we would be guessing as to what the next steps are.
Kyle method: VoLTE support progress - #142 by Kyle_Rankin
and note the comment to double check everything as you type it.
You will have the same issues with sudo and needing the password and the password’s not being echoed on the screen (for security reasons) but I guess you are on top of that now.
The first command in the Kyle method may also not be echoed on the screen. (Not sure about that.) But anyway, if the first command does not echo then don’t worry about it. Worry if the subsequent commands are not echoed.
Also, a random comment from me: It can be that immediately after you plug a modem in, the system itself is chatting furiously to the modem and you can interfere with that and it can interfere with you. So after booting up, and assuming that the modem on the Librem 5 is switched on (not killed), I would leave it for some minutes before attempting this procedure.