Sandboxing it means it doesn't have any elevated privileges like MicroG has so it gets less data. MicroG still gives Google the information they're after, just proxies through alternative services I believe.
I use AntennaPod but don't love it. It can be quite buggy. Podcast length is never correct for example and will reach the end before the podcast has finished.
I had an iPhone 12 for a couple of years but got fed up with how restrictive iOS is. I've also had a few iPads over the years but never really used them as much as I'd have hoped. My only experience with a Mac was trying to use an iMac on campus back when I was at uni and it was the slowest and laggiest computer I think I've ever used.
GrapheneOS has an incredibly easy installation as it's entirely done through your browser (though it doesn't work on Firefox unfortunately).
As for Sandboxed Google Play versus MicroG, I believe app compatibility is much better. It's not perfect as I've come across multiple apps that simply don't work on Graphene but I hear the situation is a lot worse with MicroG. There have also been quite a few instances in the past of MicroG leaking data it shouldn't be.
Happened on Arch last night and this morning switched to openSUSE Tumbleweed with the exact same issues. GPU is a GTX 1070 with nvidia drivers installed.
No nothing else is running. Just Steam. It was happening on Arch last night and I switched to openSUSE this morning and get the same problem. Both times Steam was installed through the native package manager.
By all means download from YouTube, just don't convert to MP3.
If you want higher quality then there are tools for downloading from Deezer and Qobuz.