If you plan on using third party firmware you should look at compatibility with OpenWRT BEFORE buying the device. Router manufacturers are unwilling and unable to provide a future-proof software.
Latest proof of that in my case was with a new Wi-Fi 6 router Netgear WAX206. After indeterminate time clients would just stop receiving packets and would require reconnecting. WAX206 latest factory firmware is based on OpenWRT from 2016 (Netgear still refuses to open source parts of it). After flashing current OpenWRT the connection is rock solid.