If I uncheck 'Optimize Mac Storage' do my files still sync to iCloud?
If I delete a large file from my computer does it get deleted from iCloud as well?
MacBook Pro 13″, macOS 11.6
Re the question in the title: If you uncheck Optimize Mac Storage, your files will still sync to iCloud -- the difference is that with it unchecked you will have a local copy of all of the iCloud Drive files also stored on your Mac. With it checked, some files may not have a local copy if the Mac is low on space.
Re the question in the body of the post: If you delete a file from your computer (and if that file is in iCloud Drive on the computer), it will also be deleted from iCloud.