Never use device names like /dev/sda2 - systemd loads the devices in arbitrary order - you must use a persistent identification like UUID or LABEL to avoid possible load order issues.
After you have adjusted your fstab - did you check your default grub config /etc/default/grub?
If you are/were using hibernation you may have an invalid reference to the system swap.
In any case you will need to rebuild your grub configuration
sudo grub-mkconfig -o /boot/grub/grub.cfg
While timeshift is handy to recover from when you run into intermediate update errors - it is not the best tool for restoring to bare metal (in case of disk exchange).
Other tools are better suited.
A rule of thumb - packages can always be reinstalled - when you have made system specific changes to a few specific system files - document the change so you will know what to look out for.
Backup only your home folder - everything else can be installed.
Consider using separate storage for your data - either on the same disk or more preferable on a secondary disk.
There is a couple of topics in the #contributions:tutorials section covering these scenarios e.g.