click the cogwheel and select computercomputer and make sure the steamdeck is selected if this is currently the "steamdeck" selected when it had steamOS it no longer has the same machine ID (connection ID) in steam link
I experienced the same issue when streaming from my SteamDeck and my Windows PC too. I guess it's an issue with the SteamLink itself, being end of life already. I just connect my SteamDeck, instead of my SteamLink, to my TV