Basically the title, which RP do you think is better? Obviously the RP6 has more performance but is the RP5 maybe a better deal? Or am I completely on the wrong track and should watch for an AYN Odin 2 Portal?

Budget: 250€ is the limit. Especially because Retroid etc. don't really disclose the duties, taxes, whatnot which you may need to pay when importing such a handheld so I need a buffer in my budget for a big bill from the shipping company.

Use case: I want to use this mostly as a lightweight Steamdeck alternative for indie and older titles.

And is https://www.goretroid.com/ really the official website? I don't know but all of these websites look a little bit suspicious to me.

I don't have a definitive answer to all your questions, but I can confirm that goretroid.com is the official website.

For the other Q's, I would just say that generally, if you're going to be running Gamehub Lite or Armada, you're going to want as much built-in storage and RAM as you can get your hands on. Gamehub doesn't support loading games off of SD cards right now.

I've got a few retro handhelds, but not either of these. They're great for emulation, but I'm not sure how good they'd be for running pc games. I've used portmaster a bit and found it clunky.
I think if you're primary use case is pc games, you'd probably be happiest saving a bit more and picking up a Steamdeck.
If you're more thinking about emulation, I'd probably go with the PR5. I don't think there's much that the RP6 can emulate that the RP5 can't. Also, I prefer dpad up top, but that's maybe just me.

Thank you, this alone already helps a lot!

And that Gamehub quirk is something I was not aware until now, thank you for pointing out!

Have you tried Gamenati/GamehuGamehub (compatibility layers) or ArmadaOS (SteamOS-like but on ARM)? I heard lots of good things about them. I only later on learned about Portmaster tbh.

Easier said than done, a Steamdeck is easily double the price right now. But thank you for the clarification which would be better for emulation!