After years of stalling, I finally installed OpenWrt (22.03.2) on my Linksys 3200ACM and I am loving it.
The migration was almost perfect (though a little lengthy): OpenVPN, DMZ, and almost all of my over 100 devices are working perfectly, using LAN, Wifi 2.4 and 5.0. I kept the old SSID and Key, so all devices were just popping up after I created the static leases and enabled the wireless connections. And my question here is about the "almost", of course.
I still use an old Palm TX that was working fine with the stock Linksys firmware set up like this:
802.11b concurrency has been disabled by default in recent releases, as this causes a significant performance degradation relative to 802.11g and up (this can be changed in configuration). Beyond this, mwlwifi is known not to be great at interoperability with other vendors' wifi chipsets (worst with Espressif esp8266/ esp32 wireless in many IoT devices). But without closer debugging and knowing about the specs of this Palm TX, it's mostly guess work.
I only use 2.4 for devices like light switches, thermostats, and things like that, that don't require too much band. Oh, and my Palm TX, of course .
For high throughput, I use 5.0 and I have another router with a different configuration just for wireless cameras, so they don't interfere with my regular work. The problem is that this other router is in the basement, too far from where I use my Palm, otherwise, I could use it instead of the 3200.
It's not a direct answer to your question, but if you still have old device(s) you need to connect, why not buy an old 802.11b AP specifically for that purpose? I'm sure you can find some for like $10 in most metro areas. Surely would beat wasting time troubleshooting WRT3200ACM wifi.
It's disabled. This is one of the options I tested first because I saw somewhere that it could cause issues. Just as a note, none of my other devices had any problem with this option checked except the air purifier, which lost connection but returned when I unchecked it.