Develop module shows "No File" message for everything

From your screen-clips, looking at the filmstrip thumbnails, they all show the exclamation mark [!] that indicates Lightroom-Classic has lost the link to the location of the original files. They are "Missing" in LrC terms.

Do not try to Import or Synchronize folders, instead re-link the Catalog to the correct location of the files with the method in these links

MISSING FILES & FOLDERS (Adobe link)

MISSING FILES & FOLDERS (Lightroom Queen)

Lightroom Classic version: 10.0 [ 202010011851-ef6045e0 ]
License: Creative Cloud
Language setting: en-US
Operating system: Mac OS 10
Version: 10.15.7 [19H2]
Application architecture: x64
Logical processor count: 6
Processor speed: 3.1 GHz
SqLite Version: 3.30.1
Built-in memory: 16,384.0 MB
Real memory available to Lightroom: 16,384.0 MB
Real memory used by Lightroom: 1,068.3 MB (6.5%)
Virtual memory used by Lightroom: 9,297.4 MB
Memory cache size: 3,974.7MB
Internal Camera Raw version: 13.0 [ 610 ]
Maximum thread count used by Camera Raw: 4
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Camera Raw virtual memory: 14MB / 8191MB (0%)
Camera Raw real memory: 16MB / 16384MB (0%)
Displays: 1) 5120x2880, 2) 2560x1440

Graphics Processor Info:
Metal: AMD Radeon Pro 575X

Application folder: /Applications/Adobe Lightroom Classic
Library Path: /Users/ruthfletcher/Pictures/Lightroom/Lightroom Catalog-v10.lrcat
Settings Folder: /Users/ruthfletcher/Library/Application Support/Adobe/Lightroom

Installed Plugins:
1) AdobeStock
2) Aperture/iPhoto Importer Plug-in
3) Facebook
4) Flickr
5) Nikon Teth

Also, please post a scrrenshot of your Develop Module, full screen.

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Please post your System Information as Lightroom Classic (LrC) reports it. In LrC click on Help, then System Info, then Copy. Paste that information into a reply. Please present all information from first line down to and including Plug-in Info. Info after Plug-in info can be cut as that is just so much dead space to us non-Techs.