iMac macOS unable to delete photos from macOS photos library

We have an iMac M1 with macOS sequoia 15.5 and we are unable to delete photos from macOS photos app accessed photos library.

The photos library file is not the default one, rather a separate non-default photos library file we created and maintain on a usb-c thunderbolt port connected m.2 2280 nvme ssd enclosure with pciE gen4 ssd.

The external drive is unlocked confirmed by fact that I can copy or create files on that drive and delete them. I've confirmed that signed in user has read+write permissions on this non-default photos library file in get info view. I cannot select photo in photos library > hit delete key > confirm delete and have it deleted file.

Any suggestions on what we are overlooking?