Why is internet on my PC so slow?

Hi peeps; help me with this brain buster about what the potential issue could be since i moved into my new place:

Internet is 100mbps

Phone can get full speed on wifi

PC only gets 30mbps max on wifi - drops to 300kbps for extended periods of time

Connection to 2.4ghz wifi on PC is full bar

When i connect my PC to my mobile hotspotting the wifi (which gets 100mbps), my PC can only still get around 20-30mbps despite the receiver being right next to the phone

Powerline adapter also only achieves 20-30mbps

Sides notes:

- Last place i was at (2 weeks ago), everything was fine so I dont think its the attached wifi receiver. I am on the second floor in this new place and the router is on the first floor but im not on the opposite side of the apartment or anything. Im right above the router.

- Changed channels multiple times on router settings to no avail. (used wifi analyser to choose best one)