unpacking package content in photos.

How much free space do you have on your internal drive and on the external where the 2nd library is located?

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

To examine your setup to see if there's a reason for the slowness do the following:

Download and run Etrecheck. 

Copy the report

and use the Additional Text button to paste the report in your reply.

Then we can examine the report and see if we can determine the cause of the problem.

Addendum: for reference I have a Photos library on an external SSD with 55,000 photos and 900 videos. It opens in 2-3 seconds.

This crashing thing seems like you have way bigger problems than Photos being slow. There could be problems with memory failure or hard drive failure. You need to check that out.

You should probably run the app Etrecheck that Old Toad suggested. You should also run Apple's Hardware test:

Use Apple Diagnostics to test your Mac - Apple Support

Could you tell us what OS your Mac is running?

Are you using an external hard drive? How is it formatted? Incompatible formatting could cause the sorts of things you are seeing. Also as OT suggested, '"cleaning", "optimizing", "speed-up", anti-virus or VPN apps' can cause similar problems. Have you used any of that stuff?

The only safe way to recover your images from Photos is to Export them

File -> Export -> Export Unmodified Original.

Unfortunately there is no other migration path for Bridge.

Where is your Library stored? If on an external disk, what format is that? Also what version of Photos?

Dragging from the originals folder will lose all your original file names. You need to proceed cautiously as you could experience dataloss. Do you know the name of the alternative app you're using? Is there a migration path?

How much free space on your HD?

I have the latest version of lightroom (7.4.1) The problem with Lightroom is that it migrates the photos to the cloud. I dont want such a storage.

The why are you using Lightroom? That version of LR is designed specifically for that way of working. If you want to manage your files locally you need Lightroom Classic.

Can you export anything at any setting?

Sorry not sure what you mean by "on Lightroom"? Do you mean migrate photographs to Lightroom or from Lightroom? Also which version of Lightroom? LR Classic or the Lightroom CC version?

Also how many items are you trying to export at once?