Hi @Lothaer . When you connect to your 2.4G and 5G, what is the wifi connection speed for each connection? (When connected, in Settings, tap the connection to show signal strength and speed.)
The 2.4G has greater range. Too far away, the 5G signal may be too weak for high speed. Do your testing next to the router.
There may be other activity on 5G band slowing your test or interference from surrounding networks.
These are TPG articles for wifi.
@Lothaer . I don't know what you mean by "which speed test". You've run a speed test to get those numbers in your first post. I'm talking about the wifi speed between your wifi device and the router. I explained the method for Android; Apple devices might be different.