Logitech K400 should work, I have Ergo K860 and it works on OpenBSD. There are two problems:
(1) BIOS might not be accessible,
(2) It is not possible to do pairing with receiver on BSD, this can be worked around by running HirensBoot from USB.
CC: 𝙹𝚘𝚎𝚕 𝙲𝚊𝚛𝚗𝚊𝚝 ♑️🤪 (nprofile…6cws) roman (nprofile…x8ne)