Absent remedial action, almost every 4G connection will suffer from a phenomenon known as 'bufferbloat', which occurs when there is an attempt to transfer at a higher packet rate than available given the present capacity of the connection, which causes buffers to fill up and latency to increase, rendering latency-sensitive applications unusable under load.
Fell free to test this out yourself by running a ping test to 1.1.1.1 whilst saturating your download/upload.
And try the helpful waveform bufferbloat test here:
https://www.waveform.com/tools/bufferbloat
Want to fix it? You need to place an OpenWrt router downstream of your 4G router, and use something like this:
https://forum.openwrt.org/t/cake-w-adaptive-bandwidth/135379
I am the author of the latter project, which is already used by many 4G and Starlink users to help keep latency low under load.
