After Upgrade to Catalina - Photos: The library could not be opened. Photos was unable to open the library “Photos Library”. (3146)

Same problem here. Last night tried to have Photos repair the library and ended up with the following on multiple occasions (yes, that's right 2,295% complete):

Today, tried to repair again and the app actually started "repairing." After several hopeful hours (library has over 65,000 photos), I got this:

So I'm hoping the next release of Catalina/Photos fixes the problem.

Alright everyone! I had the same issue and after an hour with Apple on the phone, we got it all figured out! (I have everything saved on iCloud so it made the process easier. If you don't have all your photos on iCloud, I would suggest calling.)

So what you're going to want to do is when it gives you the pop-up saying to select a photos library, hit that and select "create new library". It should open you up to the Photos app, but with nothing in them.

You're going to go up to the top of your screen Photos -> Preferences, click on the iCloud tab and turn on iCloud.

It should start downloading everything back into this new library. If it doesn't either plug in your laptop OR take a screenshot of the page and drag it into Photos. At the bottom, it might say something along the lines of Battery Save/Low Power mode and in blue letters "RESUME," hit resume and watch your Photos come back to life!

after this update it gives me the same error and the library is still not available anymore.

please give me a solution

Did you find one? I have exactly the same problem :-(

and so do I!!!