Which version did you install?
This is given for my install:
$ mosh --version
osh 1.4.0 [build mosh-1.4.0-dirty]
Copyright 2012 Keith Winstein <mosh-devel@mit.edu>
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
$ pamac info mosh
ame : mosh
Version : 1.4.0-3
Description : Mobile shell, surviving disconnects with local echo and line editing
URL : https://mosh.org/
Licenses : GPL3
Repository : extra
Installed Size : 674.1 kB
Groups : --
Depends On : libutempter openssh openssl perl-io-tty protobuf
Optional Dependencies : --
Required By : --
Optional For : --
Provides : --
Replaces : --
Conflicts With : --
Packager : Antonio Rojas <arojas@archlinux.org>
Build Date : Thu Jun 29 18:36:38 2023
Install Date : Tue Jul 4 17:29:52 2023
Install Reason : Explicitly installed
Validated By : Signature
Backup files : --