There’s some nuance with 5ghz, let’s talk 2.4 GHz first.

You’ve heard correctly, 1, 6, and 11 are the “non overlapping” channels, if anyone is on, say, channel 9, then everyone on 6 and 11 are going to have a bad time. But this is entirely based on everyone using 20mhz wide channels. Anyone using 40mhz wide channels are just going to fuck up the airspace. 40mhz wide channels basically occupy two of the three non-overlapping channels on 2.4ghz. never use 40mhz wide on 2.4 GHz. IMO, it shouldn’t have ever been an option.

5ghz is a UNII band, and there’s three, technically four or five, main sections of the band that are relevant UNIi 1 is the low end of 5ghz, I don’t have the channel numbers off the top of my head, but I know it ends at or around channel 90 or so? I’m tired and I’ve been ill today, so please forgive me. Some of the specifics are slipping away right now and I don’t have the brain power to cross reference it. You can look all this up anyways.

UNII 1 is pretty typical, very similar to how 2.4 GHz works, just on a different band.

I’ll circle back on UNII 2

UNII 3 is the high part of the band and the only nuance here is that the 5.8 GHz ISM channels overlap with a lot of this, so any consumer electronics like cordless phones that use 5.8 GHz, might cause problems with some of these channels. Use of the ISM band here has been on the decline for a while, so it’s probably not an issue, but something to be mindful of.

UNII 2 is a whole thing. You’ll need to look up what is allowed for your country, but some channels are off limits and this band actually interferes with radar operations, so anything operating UNII 2 channels needs to have radar avoidance built in. That’s pretty much automatic, or it should be. The key take away with these channels is that you need to let the system pick the channel or will use in the band, so that it can change the channel to avoid radar if needed. Setting a static channel on your Wi-Fi in the UNII 2 band might land you in hot water.

Some 5ghz channels can only be used indoors, some can only be used in specific countries, so look it up for your situation. Wikipedia has a comprehensive article on it, and I would encourage you to familiarize yourself with it.

6ghz regulation is starting to settle down but it’s looking to be a bit more open and consistent between countries which would be a nice change.

Also, there are different power restrictions on different channels, don’t worry yourself too much with that since most consumer access points and Wi-Fi routers don’t push enough power to exceed even the lowest restriction.

Feel free to move to 40mhz for 5ghz, there’s a lot more channels and 40mhz wide can really enhance your speeds. Stick to 20 for 2.4 GHz; but don’t feel limited for 5 or 6ghz.

Your methodology is good. But please understand that the graphs are an estimation, a real waterfall examination with an SDR that’s capable of observing the channel would be the only way to really know what’s happening in the airspace. Generally that’s overkill for residential installations. Just bear in mind, those scanner apps will only show other Wi-Fi networks. Non-Wi-Fi interference will not be shown. Don’t hesitate to try a different channel if one isn’t working great for you. Might just be alien interference (in this context, alien means non-Wi-Fi).