Hi @fmon, welcome to DevKinsta!
If closing and reopening DevKinsta doesn’t fix this, then you might have to manually clear the process. Please see if this is applicable for you: Stuck on Canceling maintenance, restore snapshot - #7 by Kevin
If you aren’t able to cancel or complete the process through DevKinsta, you will also need to contact our Live Support team in MyKinsta. They can have our Sysops team disable maintenance mode on your Staging Site.
Please let me know if you run into any issues!