Remove Very Basic 'White Soup' Clouds:
White soup ones are controlled in timecycle files ('w_overcast.xml' etc). Try messing with '<sky_cloud_gen_density_offset>', '<sky_cloud_density_bias>' & '<sky_cloud_gen_threshold>'. Test each one out independently & set all it's 13 times of day to 1.0000 or 0.0000 & you'll figure out how to make them invisible/not appear. Been a long time since I edited my timecycle, can't quite remember which need 0.0000 & which need 1.0000, but you should figure it out in a few loads of the game.

Remove 3D Looking Clouds:
OpenIV > Ctrl+F3 > Search 'mods' folder only for 'v_clouds.rpf'
Open the 'v_clouds.rpf' you find & after backing up the 'v_clouds.ytyp' files in them, replace them with this one.

That should do it

Technically, you only need to replace the file loaded by the game, but for ease of instruction, you can safely replace all that you find. If mutliple files found, they are unlikely to be identical. So make a note of where you got them from when backing up, so if you wish to revert, everything goes back in the correct place etc