SimpleX isn’t able to share your profile-data between devices. Instead you connect with e.g. the desktop app to the phone to use the phone-profile, but it need to stay online, which can be inconvenient.

With the CLI version you are able to run it on some (private) server and then connect the phone and desktop app to it. But it is still not really convenient, as you need to establish a tunnel (for example SSH port forwarding) to the server (the clients don’t support connecting via internet URL the last time I checked).

As far as I know you still need a phone number to create an account. But for connecting you can use the new usernames (and make sure to disable automatic number sharing with contacts in the settings).

SimpleX doesn’t need a phone. The desktop app can run standalone or linked to the phone-profile (but the phone must stay connected for that).
They also have a CLI version (which you can use as a central hub for your profile).

Have you tried to enable only one codec and set the default quality to something like 720p in the preferences?

Which instance are you on. I use piped.adminforge.de with uBlock and it works fine. Also the feed shows stuff from my subscriptions (I think I adjusted something in the settings for that).