Don't bother about the 'numbers'. Maximum speeds are not your primary goals, consistency and lowest latency are more important. dBm values are worthless unless you're designing your own circuits (end to end).
Change the Control Channel to anything but Auto. Reboot the router. Verify that the Control Channel you picked, sticks. Then simply use your network normally.
Take notes on important things. Like fringe areas with certain channels. And/or with certain client devices. How responsive the network feels (lower latency is always better than marginally faster speeds) for both web browsing and internal, LAN, workloads (like accessing a NAS, printer, scanner, etc.). And how stable (and responsive) the network is over a course of the day (when the neighbors come home, and the streaming/gaming starts).
Anything else you keep notes on is incidental and not important, as it won't help you get a faster networking experience any sooner or more reliably either.
The WiFi apps are great to see 'stats', but they don't do anything to improve your network (except by chance/luck and a lot of wasted time).
Remember when you're testing that you're not relying on a single client device to do all your tests with (this isn't a race). Use all the clients you have in all the areas that they are normally used and use them normally (speedtest.net and fast.com are not normal uses). These are the notes you take and compare across different channels used.
There are only so many Control Channels to 'test'. And these can be done very quickly to see what is the best channel 'now'. Once you have preliminarily decided on the best candidate channel to use, be sure you leave it for at least 24Hrs or more before you give up on it. This allows the surrounding APs (which are most likely on Auto) to move off your selected channel.
Did you read the following too, from the link, I provided above?
Control Channel Setup 2021
Control Channel Setup (more)