You need to get a dumb brick for that Rock 5B. Looks like you got one of the ones with a bad firmware. When it negotiates the power drops out. There're tons of forum posts.
I've had the HP Dev One now since shortly after introduction. It has been rock-solid and everything just worked. Also the memory and SSD are upgradable easily enough.
I used to use ThinkPads exclusively, but Lenovo's priorities for ThinkPads no longer match mine.
I've since moved on to HP Dev One. It's well-rounded for me, was easily upgraded to 64GB of ram, and came with Pop! OS out of the box. I've also used System76 machines in the past with success, but I'm rather attached to having a pointing stick.
My dayjob provides a Dell XPS 13 (factory-loaded with Ubuntu) which is an acceptable machine, but I don't travel with it much.
I always use GNU/Linux. Of late I've been sticking to LTS Ubuntu or Pop! OS releases. I'm a strange case though, because my desktop is LXDE, and all I ever really do is run a browser or two with a pile of terminals, so I'm not running heavy desktop apps like Slack, Discord, or LibreOffice.
Simple solution here: don't buy locked phones anymore. My last locked phone purchase was in 2011. In the US, you don't need to buy a locked phone anymore to get service.
I'm on a Pi4 8GB now with a 1TB USB SSD (Adata). The only issues I generally have are anxiety around Chromium staying up to date (it is still on version 98.0.4758.106 as of this writing.) and YouTube video playback can drop a lot of frames if the system is any kind of busy. I run Raspberry Pi OS 11 on it at present.
I love that it is just Ubuntu underneath, so I just install `lubuntu-desktop` and I've got my preferred desktop environment, while not losing the benefits of their kernel tuning and such.
I also used to always run ThinkPads (and Precision workstations with pointing sticks). I these days run a System76 Lemur Pro with a USB thinkpad keyboard I stick on top. The built-in keyboard is good, but trackpads and I have never gotten along. They've come a long way. Another option that friend got was the Frame Work. I helped him assemble it, and it also is a great GNU/Linux machine. Everything just works.