Hi.
I'm using Fortress + Red Dwarf ruins, but when encountering any hostile ruins nothing is claimable or minable.

And example:
Found a purple power crystal with walls surrounding it and two power poles.
Destroyed the laser turret defence and then tried to use the claimtool, but nothing happens.

Shift+claimtool removed the remnants of the turrets, but other than that nothing works.
I can hook a power pole to the crystal I found and use it even it's still market as an enemy structure, but can't mine or claim in any way.

Random ruins that's just some buildings/belts is minable, without the need of claiming anything.

I tried disabling the "Hostile ruin defenses", but only difference is that the turrets don't attack me.
"Ruin set" is set as "FortressRuins".

Typically the only thing mineable in hostile ruins is certain steel chests containing obvious "treasure" items.

A couple of the ruins layouts are bugged and have their treasure chests marked as enemy, making them impossible to claim. ...Although it occurs to me to wonder if an inserter could remove the items.

So ran into this issue too, but I found an older mod that has the solution.
The Capture Entities mod
https://mods.factorio.com/mod/capture