Hi @tangent and thanks for your detailed answer!
Here's export of wifi section
int wifi export
# 2024-06-06 13:21:28 by RouterOS 7.15
# software id = **ELIDED**
#
# model = C53UiG+5HPaxD2HPaxD
# serial number = **ELIDED**
/interface wifi channel
add band=5ghz-ax disabled=no frequency=5180,5220 name=5ghz skip-dfs-channels=all width=20/40/80mhz
/interface wifi configuration
add antenna-gain=0 country="United States" disabled=no name=home-private-cfg security.authentication-types="" .ft=no .ft-over-ds=no ssid=MikroTik-Home
/interface wifi security
add authentication-types=wpa2-psk disable-pmkid=yes disabled=no name=home-private
/interface wifi
set [ find default-name=wifi2 ] configuration=home-private-cfg configuration.mode=ap name=wifi-2.4ghz security=home-private security.authentication-types=wpa2-psk,wpa3-psk
set [ find default-name=wifi1 ] channel=5ghz configuration=home-private-cfg configuration.mode=ap disabled=no name=wifi-5ghz security=home-private security.authentication-types=wpa2-psk
I have my 2.4G interface completely disabled for now, since I don't have any IoT yet, and that was the same on previous router. I don't need this band for now, so there's no switching between, old router is powered off. I did exactly as you described - everything in config is separated from the physical interface (except for authentication types - they seem to be ignored from security config, leaving my network "open", and only setting them to the physical interface did the job. This seems like a new bug for me, bcz it worked in ROS6).
And about provided logs - at first, I just did configuration and started using network. However, I noticed frequent disconnects on the laptop, lasting for like 5-20 seconds or so to reconnect automatically. That's why I'd opened logs, and this is the events that are logged when disconnect occurs. Also, when disconnect happens, laptop shows 1/3 SSID signal strength and tries to reconnect, and when reconnect happens it becomes 3/3 again. Laptop is literally used as desktop now, with same positioning for itself and old router/new ax3. With old router I played online games no problems or disconnects.
Also have to notice that wireless quality itself is perfect until it disconnects, i.e. surfing is omega-fast and smooth, no lags for youtube or twitch (or both at once).
Things that I've also read from this forum or reddit before posting:
1. Possible antenna damage - I had my antennas attached before power on
2. Possible ROS7.15 wireless bugs - signal strength sometimes shows above zero, can firmware version be the cause of the problems?
This is the log of one of disconnect events, showing this
13:39:32 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz disconnected, connection lost, signal strength -75
13:39:32 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz disassociated, connection lost, signal strength -75
13:39:34 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz associated, signal strength 21
13:39:35 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz connected, signal strength 21
13:46:40 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz disconnected, connection lost, signal strength -76
13:46:40 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz disassociated, connection lost, signal strength -76
13:46:43 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz associated, signal strength 17
13:46:43 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz connected, signal strength 17
13:46:49 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz disconnected, connection lost, signal strength -71
13:46:49 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz disassociated, connection lost, signal strength -71
13:46:51 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz associated, signal strength 21
13:46:51 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz connected, signal strength 21
13:46:53 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz disconnected, connection lost, signal strength 21
13:46:53 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz disassociated, connection lost, signal strength 21
13:46:55 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz associated, signal strength 17
13:46:56 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz connected, signal strength 17
13:46:58 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz disconnected, connection lost, signal strength -74
13:46:58 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz disassociated, connection lost, signal strength -74
13:46:59 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz associated, signal strength 20
13:46:59 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz connected, signal strength 20
13:47:01 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz disconnected, connection lost, signal strength -74
13:47:01 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz disassociated, connection lost, signal strength -74
13:47:03 wireless,debug 0C:7A:15:F5:D2:AF@wifi-5ghz associated, signal strength 20
13:47:03 wireless,info 0C:7A:15:F5:D2:AF@wifi-5ghz connected, signal strength 20
3. Wireless interfaces are bridged but should not be - they are, but doubt it affects wireless connectivity, since I did same config in ROS6.
4. Tried to play with frequencies - leaving it blank sets channel to 5500, and SSID becomes invisible to Samsung S21