Hey, I am sorry you have had problems.
Please try moving your files and thumbnails to their desired locations first. This will 'decouple' them from the main database, making them not 'portable'. The button at the bottom moves the db and everything underneath it, which includes your client_files atm. I recommend something like this:
Update your backup if you maintain one.
Set your desired resized thumbnail location.
Hit 'move files now' and wait for it to finish.
Hit 'add location' and set your desired files location. In your case, try D:\hydrus\files to move them out from the db parent folder.
Hit 'empty/remove location' on the old (current) location.
Hit 'move files now' again.
Then do the db/install migration, either manually or through the 'migrate entire database' panel.
Update your shortcut, and try to boot.
Update your backup scheme to match the new locations.
My image is just now from my own laptop, which is similar to your situation. I would expect your final dialog to look similar.
Please let me know if you run into any more trouble or if I did not explain anything enough.
