Hi @sleepy_duck and welcome to the Manjaro community.
It may be possible to reinstall/upgrade the Grub bootloader, in which case this tutorial will be useful:
If that isn’t successful, you could try procedures outlined in this tutorial:
Of course, failing all of the above, a complete reinstallation is the final resolve.
A little housekeeping:
As a new user, please take some time to familiarise yourself with Forum requirements; in particular, the many ways to use the forum to your benefit:
- [How to] Request Support
- [How to] Post Command Output and File Content as Formatted Text
- Forum Rules
- Strict Forum Rules and Guidelines
And last, but not least, the Stable Update Announcements, which you should check frequently for important update related information.
I hope you find these links helpful.
Cheers.