Is there a way for cryptomator to save image thumbnail in the vault?

Problem: cryptomator always need time to create thumbnail after unexpected shutdown. The problem is it literally takes hours.

my laptop is old and the battery is dead. the charger have some lose connection and would shut off if moved. I don’t usually need to move it around but accident happen, no matter how careful I am.

I see cryptomator always recreate image thumbnail for image inside the vault whenever my laptop shutdown unexpectedly. There are many folder of “Cryptomator/mnt/qRJgyaVuR8sP_0”, “Cryptomator/mnt/qRJgyaVuR8sP_1”, “Cryptomator/mnt/qRJgyaVuR8sP_2”, and so on.
my throughtput is only around ~1.2Mib/s - 0.8Mib/s (I use HDD). it’s literary takes a good few hours before every image would have thumbnail.
is there a way to just save the thumbnail into the vault?

Thumbnails are created by the system, not by cryptomator.
This applies to linux as well (please correct me if Im wrong).
Based on your linux version and configuration, if you enabled the creation of thumbnails, they are stored local in a thumbnails folder. This should be ~/.cache/thumbnails.
So in your case it looks like your system is deleting these thumbnails (or even the complete cache) every time it shuts down unexpected. Because of your global system settings they are then created from scratch.
Nothing cryptomator can do about that.