A Boot Camp partition takes its space whether you use Windows or not

A Boot Camp partition is not a folder, it is a division of the disk, and it takes its full size from the moment it is created whether Windows is used or not. On an Intel Mac where Windows was installed once for a specific tool, this is frequently the largest single reclaimable item.

Check what is on the disk

diskutil list
df -h

A Windows partition appears as a separate volume, usually formatted NTFS and named BOOTCAMP. Its size is the space you would get back, and macOS shows it as unavailable rather than as used by anything you can see.

Before removing it

1. Boot into Windows once and copy out anything you need. macOS can read NTFS but not write to it without extra software.
2. Deauthorise any software licensed to that Windows installation.
3. Back up the Mac side, since repartitioning is a disk operation.
4. Check whether anything still depends on it, such as a tool with no Mac version.

Removing it properly

Use Boot Camp Assistant, which has a restore option that removes the partition and returns the space to macOS in one step. Doing it manually in Disk Utility works but is easier to get wrong, and getting a partition operation wrong is the kind of mistake that needs a restore from backup.

On Apple silicon

Boot Camp does not exist on Apple silicon Macs, so if you are on one of those and looking for a Windows partition, what you have instead is a virtual machine or a compatibility layer, both of which are files rather than partitions and are removed differently.

Other volumes you did not create

If diskutil list shows volumes you cannot account for that are not Boot Camp, they are probably part of the normal APFS layout rather than something to remove, and what the other volumes in your container are explains which is which.