When I have initially posted this I haven't noticed the OP's specific requirement not to propose
For what it's worth I'll leave it here but also confirm that the best solution is indeed the most up-voted one HERE, with variables that can be found as indicated in THIS complementary answer.
In order to do it with a GUI, I use Grub Customizer (I'm in Mint but that doesn't count here).
The simplest and most direct way (thanks @eMKi for the suggestion in comment) — best suited for a permanent setting, in General Settings > default entry > predifined, simply select the desired kernel in the drop-down list.
Or, in case one needs the "previous booted entry" to be the one selected (might be useful in dual boot with Windows when doing an Windows update that requires restart, for example) — keeping the Advanced options in the grub list in case the default list is changed within Grub Customizer:
under General settings select the default entry: previous booted entry.
Then, reboot, and during boot select the "Advanced options" entry in the grub list:
and select the older kernel
On the next reboot, the "Advanced options" item will be the one selected by default in the grub list and the last selected kernel from under there will be booted (without opening the full list of kernels).
In case Windows is used, or other option in the grub list, remember to re-do the previous procedure.