I've tried that a few times but it always defaults back to the 5.11.0-41-generic kernel.
That might be because I used Grub Customizer to load the 5.11.0-40-generic kernel.
All in all I've ended up just using Grub Customizer to default to the 5.11.0-40-generic kernel.
Thank you so much for your help @Aravisian and you too @mardijker. Its honestly such a relief to have it all working again