For mini pcie I highly recommend AsiaRF's offerings, which basically all use MediaTek chipsets. I think you'll find MediaTek has the best OpenWrt support and best Linux support in general.
They have three WiFi 6 cards:
- AW7915-NP1 - WiFi 6 4T4R, non DBDC. This is actually my favourite and I have three of them in use. But then, I don't have any 6GHz devices yet and I don't actually need DBDC. This card is exceptionally low-noise. Even with a low signal (due to wall/floor penetration) I routinely get +34dB over noise due to the low noise floor.
- AW7915NPD - WiFi6 2T2R DBDC. I have one of these for testing. Works well. It seems about 3dB more noisy than the above, but still good.
- AW7916NPD - WiFi 6E 3T3R @ 5/6GHz, 2T2R @ 2.4GHz DBDC. I have one for testing. Works well. It does draw a lot of power and can get warm, but it comes with a heatsink that works well. I have tested it with DBDC and it works well in 22.03.3, but there is a glitch with DBDC in snapshot due to current work going on with the firmware. It looks to be mostly resolved, the only issue I am currently having is with 5GHz scan, which isn't strictly required anyway. I haven't tested it as thoroughly as I have the first card, but so far it also seems to be exceptionally low noise.
The great thing about MediaTek is they are actively working with Linux and OpenWrt devs.