Imported Photos gone missing from Mac!!! PLS HELP

What about Matti's question about "more than one Photos Library"?

Do you have any external drives connected to your Mac, that you may have had connected when you imported the photos? If yes, check any external drives for a copy of your Photos Library, as well as your Pictures folder. From your initial question it looks like you have seen the missing photos last directly after importing them to Photos. Photos my a have imported them to a different Photos Library than you are using now. This can happen, if you have a an external drive connected with a copy of your library. Or, if you are keeping your library on an external drive and this drive gets dismounted, then Photos might switch to a different library. So you may want to check all your external drives for Photos Libraries and look there for the missing photos.

Do you have only one Photos library on the Mac, is it on the internal disk? Have you checked the Mac's backup?

Which Mac backup? If you mean the Time Machine, I haven't been able to set that up.

Bummer. All disks eventually fail so backups are essential if they contain valuable data.

Have you checked Photos library's Recents and Imports if they contain the missing image import sessions? Sometimes images might have wrong dates and are put in unexpected places among old images.

You did not mention, if you have checked the Hidden album.

And have you checked, if Photos has created bursts ? Photos taken in quick succession may be stacked as one burst of photos.

To get started with a backup: Back up the library in Photos on Mac – Apple Support (UK)

At least drag the Photos Library occasionally to an external drive to save a copy.