So – thank you for your help, zolw 
Back to business… Yes tumbleweed is the “master” OS (I tried to say that in my very first post); Windows and Mabox are kind of slaves. On start-up suse’s grub menu offers all options. For several years all went well. Now something is broken with Mabox.
lsblk -s
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
loop0 7:0 0 218,4M 1 loop /snap/gnome-3-34-1804/90
/snap/gnome-3-34-1804/90
loop1 7:1 0 219M 1 loop /snap/gnome-3-34-1804/77
/snap/gnome-3-34-1804/77
loop2 7:2 0 81,3M 1 loop /snap/gtk-common-themes/1534
/snap/gtk-common-themes/1534
loop3 7:3 0 91,7M 1 loop /snap/gtk-common-themes/1535
/snap/gtk-common-themes/1535
loop4 7:4 0 260,7M 1 loop /snap/kde-frameworks-5-core18/32
/snap/kde-frameworks-5-core18/32
loop5 7:5 0 116,8M 1 loop /snap/core/14784
/snap/core/14784
loop6 7:6 0 289,8M 1 loop /snap/kde-frameworks-5-core18/35
/snap/kde-frameworks-5-core18/35
loop7 7:7 0 164,8M 1 loop /snap/gnome-3-28-1804/161
/snap/gnome-3-28-1804/161
loop8 7:8 0 55,6M 1 loop /snap/core18/2721
/snap/core18/2721
loop9 7:9 0 116,8M 1 loop /snap/core/14946
/snap/core/14946
loop10 7:10 0 4K 1 loop /snap/bare/5
/snap/bare/5
loop11 7:11 0 164,8M 1 loop /snap/gnome-3-28-1804/194
/snap/gnome-3-28-1804/194
loop12 7:12 0 55,6M 1 loop /snap/core18/2714
/snap/core18/2714
sda1 8:1 0 118,6G 0 part
└─sda 8:0 0 119,2G 0 disk
sda2 8:2 0 635M 0 part
└─sda 8:0 0 119,2G 0 disk
sdb1 8:17 0 80G 0 part /var
│ /usr/local
│ /tmp
│ /opt
│ /srv
│ /root
│ /boot/grub2/x86_64-efi
│ /boot/grub2/i386-pc
│ /.snapshots
│ /snap
│ /
└─sdb 8:16 0 232,9G 0 disk
sdb2 8:18 0 40G 0 part /home
└─sdb 8:16 0 232,9G 0 disk
sdb3 8:19 0 8,1G 0 part [SWAP]
└─sdb 8:16 0 232,9G 0 disk
sdb4 8:20 0 2,5G 0 part /boot/efi
└─sdb 8:16 0 232,9G 0 disk
sdb5 8:21 0 58,6G 0 part /drives/db_Digikam
└─sdb 8:16 0 232,9G 0 disk
sdb6 8:22 0 43,7G 0 part /drives/Karton
└─sdb 8:16 0 232,9G 0 disk
sdc1 8:33 0 58,6G 0 part
└─sdc 8:32 0 465,8G 0 disk
sdc2 8:34 0 232,9G 0 part
└─sdc 8:32 0 465,8G 0 disk
sdc3 8:35 0 135,2G 0 part
└─sdc 8:32 0 465,8G 0 disk
sdc4 8:36 0 39,1G 0 part
└─sdc 8:32 0 465,8G 0 disk
sdd1 8:49 0 298,1G 0 part
└─sdd 8:48 0 298,1G 0 disk
blkid
/dev/loop1: TYPE="squashfs"
/dev/sdd1: LABEL="Backup_Homes" UUID="394e4ed9-fdbd-4aa5-b5c6-e3f09c37f434" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="cfbd418a-01"
/dev/loop8: TYPE="squashfs"
/dev/sdb4: UUID="C43C-EF04" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="66f2fdb8-aa7f-45b6-b4f7-6b7714b1d30e"
/dev/sdb2: UUID="68a89f76-30ec-468a-b92e-627f3c900d4e" BLOCK_SIZE="512" TYPE="xfs" PARTUUID="79e01f9d-557f-455d-8f5f-a5537a95fcab"
/dev/sdb5: LABEL="db_Digikam" UUID="60477a50-f5fe-43e6-bed0-81317c243f72" BLOCK_SIZE="4096" TYPE="ext4" PARTLABEL="db_Digikam" PARTUUID="da52adb5-80b5-4b3e-a0e5-40d9c70f5a56"
/dev/sdb3: UUID="91555ea7-604c-42e0-bb9a-0322ea43fc1b" TYPE="swap" PARTUUID="ca1269d6-7846-4400-801d-d7ddad3a3e63"
/dev/sdb1: UUID="a2e79ec2-6ff7-4a5c-b6d0-ce339dae8f72" UUID_SUB="19f0bf60-e0e8-4ae1-a9b1-2897f670af6c" BLOCK_SIZE="4096" TYPE="btrfs" PARTUUID="e0f4378d-0b66-4396-acd9-d57673f54ce1"
/dev/sdb6: LABEL="Karton" UUID="9cbb87bf-00c9-47e6-a52e-120e64ce2872" BLOCK_SIZE="4096" TYPE="ext4" PARTLABEL="Karton" PARTUUID="f7b73e20-6418-4d1e-bc89-ddad69f89348"
/dev/loop6: TYPE="squashfs"
/dev/loop4: TYPE="squashfs"
/dev/loop11: TYPE="squashfs"
/dev/loop2: TYPE="squashfs"
/dev/loop0: TYPE="squashfs"
/dev/loop9: TYPE="squashfs"
/dev/sdc2: LABEL="WNDWS_Games" BLOCK_SIZE="512" UUID="748CEBE50746B333" TYPE="ntfs" PARTUUID="69c3c599-02"
/dev/sdc3: LABEL="LNX_DTN" UUID="45de859b-0a86-4813-86da-fae1940e22cd" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="69c3c599-03"
/dev/sdc1: LABEL="Mabox_Home" UUID="0f6d291d-9b19-42ad-bf65-7dff0ffb35b3" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="69c3c599-01"
/dev/sdc4: LABEL="Mabox_Sys" UUID="bd5e7ebc-7f64-4745-ba00-6329b39159fd" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="69c3c599-04"
/dev/loop7: TYPE="squashfs"
/dev/sda2: BLOCK_SIZE="512" UUID="82AA13DDAA13CD13" TYPE="ntfs" PARTUUID="16ece2ba-7f03-4bb8-9b73-61faabf10012"
/dev/sda1: LABEL="BOOTCAMP" BLOCK_SIZE="512" UUID="E6F6DE30F6DE00AB" TYPE="ntfs" PARTLABEL="Basic data partition" PARTUUID="8e932edf-3c3d-42fe-ae39-ef20664146bd"
/dev/loop5: TYPE="squashfs"
/dev/loop12: TYPE="squashfs"
/dev/loop3: TYPE="squashfs"
/dev/loop10: TYPE="squashfs"
Unfortunately I am unable to apply the last command. It results in:
sed: -e Ausdruck #1, Zeichen 1: Unbekannter Befehl: »�«
which means: sed: -e expression #1, character 1: unknown command: »�«