Some time ago I had issues with the space on my harddrive. Without hesitation and thinking much I deleted some big data, mainly logs or that I thought.
My sytem is a Mint 20.04 and has time shift build in by default.
That means that all system and configuration is saved.
So I booted with a USB stick an Ubuntu 20.04 live image, downloaded the deb package instaleld timeshift.
After that I could recover the most recent configuration and boot into mint again.
For the record, there is also a possebility to restore Grub: Trotzdem hier eine Anleitung für grub recovery mode.
In this case it did not sole the issue.