Windows cannot access EXT4 or BTRFS by default. Also in Linux you can use LUKS to have your partition encrypted, and Windows even with a ext4/btrfs driver will not be able to read your data.
Of course Windows, if infected, could wipe your partition table or things like this.
I am using Linux since the 90s, used Ubuntu a lot at one time, then started using MX linux, 16.1 iirc was my first install. Then I continue to use it, I have always like Xfce (coming from mwm and such), and no systemd, no snap, no flatpak etc. MX is very stable, use the latest package in .deb format. I am using it for almost 10 years now, 24/7, I am using it as my work PC too.