Since this sub gets questions about this a LOT, just dropping this here, if this violates rules you can delete it.
Wifi is broadcasted in radio frequencies, the ones that move slower go through objects better, these frequencies are the most common.
2.4 GHz travels the farthest, has the most penetration but is only between 100-300 Mbps (bits NOT Bytes)
5GHz faster with less congestion but is prone to interference and struggles to go through walls an doors has faster speeds, often up to 1 Gbps but only works well in the same room as the router
6Ghz barely penetrates walls, and is only really useful when you are in the same room with NO obstructions
Things to consider
Repeaters - These will broadcast an additional SSID (Wifi name) once these are set up, I like to mark it as _EXT. you will want to place it closer to the router and have it connect at 5Ghz then broadcast at 2.4. This are mostly setup via an ethernet cable, and once they are configured you just have to plug it into a wall outlet and it connects.
Better antennas - This helps with penetration, buy a better model and use it as an Access Point, most of the time you can just connect this directly to your router.
Heat Maps - These are what is used to map out wifi coverage in a given area you can download various options for this to test out your wifi
Multiple access points - You can buy 2 or more access points and place them on opposite sides of your house for full coverage, some devices allow you to join them together to create a mesh. You can use an old router in "AP" mode which most of the time means disabling DHCP, assigning a static IP on the same subnet and giving it the same network name and password.
Feel Free to add in the comments