This is somewhat between ridiculous design and an actual bug:
There is no extra settings button for adjusting texture resolution, instead it is hidden in the “master quality” settings button.
A lot of users (especially 144 and 4k) will have to set master quality to ultra and then set all the (unoptimized) “killer options” which are found further below in the settings-menu to lower values (lightning, occlussion etc) to get the best result.
On a second thought, one might think that “Terrain Quality” should adjust terrain texture resolution: However, it doesn’t.
I couldn’t figure out what terrain quality actually does. It’s also confusing that master quality to “ultra” will set terrain quality to “512MB” (which is low?) and master quality to “very low” will set terrain quality to “unlimited” (which is high?, at least hypothetically… again: I can’t see any visual difference caused by Terrain Quality)