Currently windows versions 23H2 ( update kb5044285 and beyond ), as well as 24H2 are unsupported. If you are on one of these versions you need to downgrade. Refer to this to check your windows build https://youtu.be/9tN3cf7jx34
im experiencing the same issue. when i load the skins and play some matches my fps still good (300+) porem it looks like I'm playing at 30 fps. However, when i just load steam without the skin changer it's completely normal