As a general rule, always reformat new drives before use.
Start with GUID partition map. If you’re using an SSD, format APFS. If it’s a mechanical drive, use HFS+.
macOS and FCP utilize many of the features of APFS, and that file system was designed to take advantage of SSDs. While Apple says you can use APFS on a mechanical drive, my experience says don’t do it. Things will be measurably slower, constant seeking/thrashing, it’s just a bad deal (even if it does technically work).
It should also be noted that FCP can behave unpredictably if you’re working off an ExFAT drive, due primarily to the lack of certain file system features/journaling. Again, do not work off an ExFAT drive with FCP. You will lose work at some point.