I have now moved my ps4 to my room and also have good values of 20Mbit / s download and 1.9Mbit / s upload (50k line). However, the upload fluctuates so much, sometimes I only have 20 kbit / s.
Just want stable internet.
Do you have any tips?
Do you have the option to lay a LAN cable?
Not currently because I'm sitting in the basement and the router is one floor higher
That is inconvenient.
You could set up another router or WLAN access point on the first floor, as precisely as possible above the PS4, and connect it to the main router via a LAN cable. For example: https://www.amazon.de/...B001FWYGJS
Then a sufficiently strong signal will probably arrive at the PS4. If not, you could get a third router, which you connect to the PS4 via cable. You then mount it in the basement directly under the ceiling, so that the distance between the two routers is as small as possible. These routers also have significantly larger antennas than most repeaters, which improves reception.
But if you want to have a very good connection, you could use something like this here. https://www.amazon.de/...B07CN58LW4
These things are said to have a range of 15 km outdoors. So should also come through very thick ceilings. But that's probably a little over the top.