Mount APFS Volume to /Users with the Disk Utility during the installation
Solution 1:
Not with Disk Utility (can't specify custom mount points with Disk Utility) but the macOS installer environment has Terminal. With Terminal, you can run:
mount_apfs /dev/disk1s3 /Users
Replace disk1s3 with the identifier of the volume to mount there.
This should answer your question about mounting during installation, but after a reboot your disk will be unmounted and /Users unavailable. To permanently set a mount point, you'll have to mess with fstab.