I have no experience with Open WRT, but I can confirm that, TP-Link Archer A7 is working great with DD WRT.
I can vouch for TP-Link wireless products in general. So far I've used 2 routers and 2 usb adapters (even drivers are working fine with Windows 11 and Ubuntu MATE) from TP-Link, and none of them had any problem whatsoever.
Regarding performance of Archer A7-V5, I'm getting full 100 Mbps (my ISP connection speed) through this router on my phone, and this is 3rd router in my setup. First being ISP, then ASUS and then Archer A7.
I'm running Archer A7-V5 for over a year with DD DRT. In fact, I've just upgraded it to July 8, r53221 build right after reading your post. Firmware files for r53221.
Ubuntu MATE. I love its simplicity, and the fact that it's based on Debian.
Also, UbuntuForums and AskUbuntu are great places to find help.