I do not have backup files, but I have all the projects files.

The story is

1. My old win10 system goes wrong, many things did not work. I have to reinstall a new one. For data safety, I keep all the data in driver C, and install the new OS in a new hard driver. Guess what? The new hard driver was used to be the driver saving Davinci backup...

2. After new system is installed, I copy all the projects files to the new driver. Davinci did not recognize them. None of them is shown in the project panel.

3. I am using 18.6.2 in both old and new system.

4. In old system, my projects are under following path
C:\Users\username\AppData\Roaming\Blackmagic Design\DaVinci Resolve\Support\Resolve Disk Database\Resolve Projects\Users\guest\Projects

But in new system, the projects are changed to following path
C:\Users\flep\AppData\Roaming\Blackmagic Design\DaVinci Resolve\Support\Resolve Project Library\Resolve Projects\Users\Projects

Same Davinci version, but the path is changed?

5. I tried to put the project files under old or new path, does not work.

Anything wrong?
Anyone can help me, please!

The situation just like following post
viewtopic.php?p=801389#p801389

Tom Jobbins says that he fix the DB with "vacuum".

I have PM him about how to do that, no reply yet.

Anyone can help me? Thanks.

I have essentially the same issue, although I'm on LInux, and I want to upgrade from free to Studio at the same time.

Something unrelated killed my host OS installation and I took the easy route to fixing it: buy a new SSD, make a fresh OS installation, copy all the files back into place from the old drive.

The directories / files I've noticed so far are as follows
In "user space":
$HOME/Videos/Resolve Project Backups
$HOME/.local/share/DaVinciResolve
$HOME/.local/share/Welcome to DaVinci Resolve
$HOME/Documents/BlackmagicDesign

And the system installation:
/opt/resolve
/var/BlackmagicDesign

What I did was:
Copy all the user-space files into place (along with all my media etc, though those were already in place since they were on other drives that did not get replaced--I simply ensured they were mounted in the same place)
Install the new Resolve Studio
I noticed that the contents of the directory:
~/.local/share/DaVinciResolve/Resolve Project Library
was essentially empty, but originally had a bunch of stuff in it. That stuff had, apparently, been overwritten by the installation process.
I moved the new directory to a different name (so I could recover it if necessary) and then copied the contents of that directory back into place from my old drive.
Restart resolve, and there were my projects, all working, with media and everything

Hope this helps