I found an mistake regarding permissions for user on server. This might be reason. Otherwise, the Synology server do not give any access or even visibility to root directory nor offer a bash. I need to search for it.
Most important are that H and I drive work.
Now I handle them via bookmark. Is it possible to automount them, so they are available from boot as drive?
Hi
Yes, have a look in Section 34.4 it explains how to add for various scenarios;
https://documentation.suse.com/sles/15-SP1/html/SLES-all/cha-nfs.html#sec-nfs-configuring-nfs-clients
So, let’s pull it together:
I use SMB in past. This works smooth with all type of Systems (WIN, MAC, LINUX) via Samba, but is slower.
I used NFS as book mark. This need setup on both server and client but works well.
NFS bookmark looks same way.
When NFS setup and fstab as well you might see it on your SLE as this:
hans-christoph@LINUXSLES:/mnt> ls h i x hans-christoph@LINUXSLES:/mnt>
There are below mnt 3 server drives mounted h, i, x
When you just pull them into Files (Dolphin) it looks like this:
Your server drives are there directly. The connection is fast as if it was a local drive and mounting is automated.
As you can see, I have still a net connection via [davs://dav.mailbox.org/] to my personal cloud at www.mailbox.org
This is better what Windows can. 
This works fine. But why does the drives (h, i, x) stick to the mouse when I klick on them? how can I avoid that?
Hi
You need to hide them with a udev rule… I have three disk showing in Nautilus
Before: 
lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 1 119.2G 0 disk
??sda1 8:1 1 260M 0 part /boot/efi
??sda2 8:2 1 16M 0 part
??sda3 8:3 1 60G 0 part /run/media/user/opensuse151
??sda4 8:4 1 4G 0 part [SWAP]
??sda5 8:5 1 54.5G 0 part /run/media/user/2E1E90951E9057A3
??sda6 8:6 1 519M 0 part
sdb 8:16 1 111.8G 0 disk
??sdb1 8:17 1 60G 0 part /
??sdb2 8:18 1 20G 0 part /data
sdc 8:32 1 931.5G 0 disk
??sdc1 8:33 1 931.5G 0 part /run/media/user/stuff_other
vi /etc/udev/rules.d/99-hide-disks.rules
KERNEL=="sdc1", ENV{UDISKS_IGNORE}="1"
KERNEL=="sda3", ENV{UDISKS_IGNORE}="1"
KERNEL=="sda5", ENV{UDISKS_IGNORE}="1"
udevadm trigger
umount /dev/sda3 /dev/sda5 /dev/sdc1
After umount (or on reboot): 