Router location is very important. Small changes make a difference. Higher, lower, direction facing, moving it left or right, and position of the antennas. The 2.4 GHz will give you more distance and the 5 GHz will give you more speed. You may have interference from other things. A lot of none WIFI things is the same bands as WIFI. You can try using a specific channel and bandwidth. Other items on the WIFI can affect the speed of other devices. This may help a bit https://www.cnet.com/how-to/home-networking-explained-part-1-heres-the-url-for-you/