Plug a USB lead from phone to computer.
Then turn off phone.
Now restart with power button and volume up.
Then you will be in boot menu.
Scroll up/down using volume keys and select clear system cache.
Now restart.
Your WiFi speed and your Internet speed are 2 different things.
If your WiFi is 2.4 GHz it can deliver a typical over-the-air max speed of up to 100< megabits per second (Mbps). 5 GHz can deliver up to 1 gigabit per second (Gbps). 6 GHz can deliver up to 2 Gbps.
And WiFi 7 8gbps.
You probably need to restart your broadband hub/router
And test again if you are still getting a slow speed call your Internet provider.
Also try using SPEEDTEST by OOKLA from play store.
And try using different test servers. Some work better than others. Also try at different times and see if that makes a difference.