Don’t sign into your server. If your server is signed in, that implies you want to limit access to a particular Plex account, so we have to authenticate it’s you when using a client. Keep in mind that Plex Web is what manages your server. Without authenticating it’s you, anybody on your network would be able to access your server and change anything they want.
As I said in my other response, Old topic : plex without internet connection, you only need to do this once per client.
And after you’ve done it once, there is a setting that you can set to allow other clients to access without needing to authenticate. If PMS is running on your PC, you cannot exclude the PC itself.