ermo
dear ermo,
thanks for your support!
why did i not follow your instructions?
someone in the Manjaro-Forum wrote that its not good to just erase the master boot record. there always should remain a partition table + bootloader to not damage the whole disk. so it is advised to better overwrite the contents with new info than delete them.
today 2 tries to install Solus, but again the Solus-installer always only created a GPT Partition Table on the Master Boot Record. I assume this is the reason why my laptop is unbootable from that.
re-installed Manjaro and the Manjaro-installer creates a MSDOS Partition Table on the Master Boot Record and MBR-bootloader. from there Manjaro boots into a GRUB without problem.
As the Solus installer only creates GPT partition table on my MBR master boot record, my conclusion was that it would have made no difference if i had followed your instructions to erase the master boot record or not, because the system ends up unbootable in any case, wheter i had erased the MBR before or not.
the Manjaro-installer delivers MSDOS partition table out of the box.
if you have any more ideas what i could try...