NixOSKDE plasma 6 kept crashing and freezing

Everything: firefox, system manager, etc.

The whole system will freeze after few minutes of use and unable to even switch to tty1.

Furthermore, I installed noto-Sans and still got tofu fonts.

Here are some photos and I do not know what caused it and how to fix it.
Please help.

You’ll want to seek assistance from a NixOS related source. Most of us here may not even understand what these images mean or what they are from.