18.04 - Cannot boot with old kernel after kernel upgrade

I have used Ubuntu Kernel Update Utility to install Kernel 5.0.5.

Some important modules won't work with it, so I wanted to boot with my old Kernel 4.20.17. However, when I select it in the GRUB Menu, I just see a blank black screen. If I select the Kernel 4.20.17-recovery then all I see are these two lines and then it hangs:

Loading Linux 4.20.12-042012 generic ...

Loading initial ramdisk ...

and then it hangs.

I removed my nvidia driver and reinstalled a newer version, and disabled secure boot. Thats all I did in Kernel 5.0.5.

Any advice how I can boot my old Kernel? Here is the log file of my last boot. I do not really understand much of the log file, but I found this section:

Mär 30 12:05:06 adam-MS-7A63 kernel: Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.20.12-042012-generic root=UUID=2ade97f2-18fd-40fb-a5ac-612aebdec8b7 ro recovery nomodeset
Mär 30 12:05:06 adam-MS-7A63 kernel: You have booted with nomodeset. This means your GPU drivers are DISABLED
Mär 30 12:05:06 adam-MS-7A63 kernel: Any video related functionality will be severely degraded, and you may not even be able to suspend the system properly
Mär 30 12:05:06 adam-MS-7A63 kernel: Unless you actually understand what nomodeset does, you should reboot without enabling it

Is this maybe the issue?

Any help highly appreciated! I slightly panic.