If your speed drops because you hit a monthly cap it likely affects all the machines. It likely is somehow limited by the internet account so everything going to the house will have the same limit.
That is a strange cap you do not see it much except on mobile broadband. Then I noticed from your speedtest it is likely you live in Mauritius, which seems to be out in the middle of the ocean. These island countries tend to still have somewhat limited fiber bandwidth to the outside world so the ISP tend to also offer much more limited plans that you see places where it is easy to get fiber.
In the end there is really nothing you can do to get past a data cap other than maybe pay the ISP more money if that is even a option of
Internet speed test. Some ISP when the bandwidth is very limited also have a total cap they are allowed to use . They can not actually even sell unlimited plans unless the connection they have is also unlimited.