• Theoretically Yes, if your Linux partition is not encrypted, any OS can read it. Password protecting it doesn’t do anything to conceal your data, just keeps people from logging into your system while Linux is booted. If this is a security / privacy related question, there is nothing to stop a program running under Windows from reading the data on your Linux partition except

• Practically No, depending on the filesystem you chose (if you went with the default, it’s likely ext4 but could be something more exotic). Out of the box Windows lacks the software / drivers to read most Linux filesystems. If this is a “can I access my files” question, you probably need to install something like this to read your data from Windows. Note that the reverse is not true. Most distros other than light weight distros like Alpine are perfectly able to read the NTFS file system out of the box. Sometimes they can’t write to it unless you install additional tools (like OOTB Debian probably can’t, but I’m pretty sure OOTB Linux Mint can if you change a setting and IDK about OOTB Ubuntu / Fedora / Arch).

The easiest way to share data between Windows and Linux is with a 3rd partition formatted to FAT32, as both Linux and Windows have no problem reading from / writing to it without additional software.

EDIT: The other poster is absolutely correct. The modern way to do this is with exFAT. What can I say? I’m a crusty old engineer.

It’s very likely that adware / spyware / malware targeting Windows users will NOT be able to read Ext4 or other Linux filesystems, unless it’s specifically targeted to do so, so you do have that added “security through obscurity” protection.