Dualboot only finds Windows after Clonezilla restore

so some facts:

• Had a dualboot installed on my laptop with Windows 10 and Ubuntu 20.04.
• I got a new SSD for my laptop, increasing the internal disk space size from 512GB to 2TB.
• As there is only a single SSD slot in my laptop I had to replace the SSD.
• I used clonezilla to clone the whole 512GB SSD to an image on a external storage.
• I replaced the 512GB with the 2TB SSD
• With clonezilla I cloned back the image from the external storage to the 2TB SSD.
• When booting now the internal SSD, it directly starts Windows. No different boot options anymore.
• The problem: The Ubuntu partition seems to be there, however I can't choose to boot from it.
• I used an Ubuntu live and tried 'boot-repair' (for which I have the paste bin ), however, it doesn't even show the 'repair' button.

Now I am a bit stuck how I should continue. In my understanding it just doesn't find the 'old' grub section to boot from. Do you have any idea how to fix these issues and re-enable booting into Ubuntu as well as Windows?

Any help is highly appreciated. Thank you very much.

Solution 1:

I've found some explanation of what might have cause your problem:

Clone entire disk to image using clonezilla and keep bootloader(s)

And here's a guide to restore the MBR so you can choose the OS once again, you will need a live USB

https://askubuntu.com/questions/88384/how-can-i-repair-grub-how-to-get-ubuntu-back-after-installing-windows