Unwanted root (/) access without sudo

I have just discovered by accident that my account, which is the administrative (only user) account on the system, has write permission on the root (/) directory without having to use sudo. That scares me. Can I do something so that the file system refuses write access unless I explicitly (sudo) ask for it or log in as root?

I am on Mint 20.3 una, Linux HPL-XFCE-20 5.4.0-159-generic #176-Ubuntu SMP Mon Aug 14 12:04:20 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux.