Ho to get the hex npub? Use a client that lets you copy the npub of a Nostr account you want to follow. Then paste it in https://nostrdebug.com/converter and convert it to hex.

https://mostr.pub has a search function to find fediverse accounts but it cannot be used for the reverse case. Also I don't know if all Nostr accounts appear on mostr.pub.

May be nostr:npub108pv4cg5ag52nq082kd5leu9ffrn2gdg6g4xdwatn73y36uzplmq9uyev6 can clarify?