Boot Camp: The startup disk does not have enough space to be partitioned
That 715.8 GB &quot;Macintosh SSD - Data&quot; looks to be a remnant of Catalina. Catalina creates a System disk and a Data disk and uses firmlinks to make them appear as one drive in Finder.  But the System disk is read only.
Meanwhile your macOS High Sierra volume is using only that volume for everything.
I think if you delete the APFS Volume Macintosh SSD - Data 715.8 GB disk1s1 you'll have enough free space.  You backed up your data right?