NTFS is fine in Linux. I have a dual-boot setup for when I need to run or test something in Windows, and I use my Windows install drive as a Steam library in both. When I swap back and forth Steam occasionally does a file integrity check, but I don't typically have to redownload anything as far as I can remember. The only caveat is that if a game has both a Windows version and a Linux version I have to set my Linux library to use Proton for the game instead of the native Linux version, otherwise, yeah it'll see the files are wrong when I switch and redownload.