I use both OpenWRT for my newer router and DD-WRT for an older router (802.11n) that’s being used for my building’s HOA. Both work great for me. No stability problems. However, I’m not using Wireguard with either of them. It’s mostly fairly basic functionality.
Not that I’m against doing this, but just so people are aware, running LTSC or IoT is essentially a violation of EULA unless your license of Windows is Enterprise or Education. Home and Pro aren’t valid for this. Yes, there are activation scripts available online, but personally, if Microsoft doesn’t want me to run Windows, it’s their loss, not mine.
What I did when I was looking for a newer router to run OpenWRT was to look at their supported hardware list, narrow down to the ones with recent WiFi protocol support (in my case, WiFi 6), then compared prices. I was able to buy a used Belkin router for $20 on Ebay that did the trick.