If you don't want to trust any client, you can write your own, it's quite simple! or audit one that's open source, I think they basically all are .

Other than that you should be fine, i think there is more risky stuff running on your machine.

As far as umbrel goes, i heard that it's communication is unencrypted, and basically relies on your network not being compromised ( if it's on the same network as your public Wi-Fi, that's probably not great). So maybe running it in a separate network and using vpn to Access it might be a good idea. I don't know enough about that though, so please don't take my word for it.