Filenames and titles do not display in All Photos..

If you're interested in batch changing Titles of photos give these AppleScripts a look:

• Batch Changing: Scripting Date and Time
  • léonie: Script: Batch Change the Date and Time to a Fixed Date (December 16, 2018)
  • léonie: Script: Lift and Stamp all Metadata from one Photo to All Other Selected Photos (Dec 14, 2018)
  • Steven Weyhrich's Script: ApplesScript to batch change date of scanned photos based on filename - reformatted (May 29, 2020)
  • PhillipU: Script to automate setting dates in Photo from the Filename - Apple Community
• Batch Changing: Scripting the Title
  • léonie: Script: Batch Change the Title of selected Photos to the Description/Caption - Apple Community (January 3, 2021)
  • léonie: Script: Batch Changing the Title to the Capture Date 2018, old version: Script: Batch Changing the Title to the Capture Date (December 23, 2018)
  • Old Toad: Batch Change Title to Capture Date-Description-Padded Sequential Numbers
  • léonie: Batch Change Title to Capture Date-Location-Description-Padded Sequential Number (July 7, 2020)
  • Old Toad: Batch Change Title to Text w/Padded Sequential Numbers
  • léonie: Script: Batch Changing the Titles to the Filenames with Extension (Dec 19,2018) (old version: Script: Batch Changing the Titles to the … - Apple Community)
  • léonie: Script: Batch Change the Title of a Photo to the Filename Followed by the Existing Title (May 25,2020)
  • Ken: Script: Changing the Title to the Filename without Extension
  • léonie: Script: Batch Change the Titles to a Given String
  • Old Toad: Append Keywords to Title Field - Léonie's Script

These and other scripts can be found in this user tip by léonie; Thematic Index to Photos for Mac related User Tips

Many of the script compileds as an applications can be downloaded from this tutorial site:  P01 - Applescripts from Photos’ User Tips Compiled as Applications  

Do you see the Titles or file names in other views, like albums?

Where is your library located? If on an external drive how is the drive formatted and connected to your MacBP?

Try this: as a test launch Photos with the Option key held down and create a new, test library.  Import some photos and test to see if the same problem persists. Does it? This tells us if the problem is limited to your current library or is more wide spread. Then open your current library and check to see if the problem still persists.

FWIW Photos libraries must be on a volume formatted either APFS or OS X Extended (journaled) that's connected directly to the Mac via cable.

Are you backing up the library or just image files to your NAS? If it's the library you had better try to recover it once to make sure it will still work. NAS drives are not formatted for Photos Libraries.