DNS problems and 5G Wireless could not start. Could you please look at the screenshots of my config?

The limit is invalid -- start = 2, limit = 254 --> this means that the DHCP range is set from 2-255. Since 255 is the broadcast address on a /24, this is potentially an issue. The limit can be at most 253 in this case.

It would also be helpful to know what specific symptoms you are seeing, what tests you have run, and the results of each of those tests.

DNS issue seems to be not there, but 5G could not be enabled...
What kind of tests I need to run?

So, you meant the limit should be 253?
As current value is 254.

Yes. Limit must be 253 or lower.

Try changing the channel selection from auto to some specific non-DFS channel.
If there is no difference, try setting the country code to "driver default".

My issues were completely resolved, as it seems.
Thanks to @mk24 @psherman @pavelgl, all of your recommendations have been applied.
Guest account configuration seems to be tricky, I would accept that.
@WereCatf Sorry for bothering you much.
Thank you all.
I could post the latest config for further reassurance, as DHCP for Guest seems to be a question for me, as I don't try it yet.