Please help with automatic NFS mounting

[rjalex]

I need to mount a NFS share from a Debian box and the manual procedure works quite well:
sudo mkdir /Volumes/rpimedia
sudo mount -t nfs -o rw,vers=3,nolock,resvport 192.168.1.18:/4TBHDD/download /Volumes/rpimedia

one first thing I do not understand is that after mounting the rpimedia has wrong ownership:

bob@RJA16 ~ % ls -l /Volumes
total 8
lrwxr-xr-x 1 root wheel 1 Dec 8 08:22 Macintosh HD -> /
drwxrwxr-x 14 _appstore 1000 4096 Dec 6 22:27 rpimedia

even though the NFS export is performed as:
/4TBHDD/download 192.168.1.0/24(rw,sync,no_subtree_check,sec=sys,root_squash,anonuid=501,anongid=20)

with the anonuid and gid being correct for my main user bob:staff

second thing I do not understand is that when I umount the /Volumes/rpimedia mount its mountpoint is gone, deleted

third mistery is that I tried setting up a permanent mount on the Mac with /etc/fstab:
bob@RJA16 ~ % cat /etc/fstab
192.168.1.18:/4TBHDD/download /Volumes/rpimedia nfs rw,vers=3,nolock,resvport 0 0
(no other lines in fstab)

but if I try a sudo mount -a (after manually recreating the mount point)
bob@RJA16 ~ % sudo mount -a
mount_apfs: volume could not be mounted: Permission denied
mount: / failed with 66

and while the NFS mount works I also get that weird mount_apfs error

Thanks for any help