cannot read photo DVD

Some guesses as to possible causes of the problem:

• The optical disc may have gone had. People once thought of optical discs as "lasting a lifetime", and I believe that those stamped (not burned) in factories, for the most part, do. However, recordable ones that have a dye layer that you burn with a laser may have a shorter life, especially if not kept in a climate-controlled place.
• The drive in the MBP may have gone bad.
• The drive in the MBP may need cleaning – though I'm not sure how you would do that safely.
• The optical disc may need cleaning. Take a dab of dishwasher liquid (for washing dishes by hand), dilute that with water, clean the disc with the diluted mixture, then rinse the disc thoroughly and allow it to dry off before placing it in the drive. (You don't want to introduce water in there!).

Probably not HFS ("no +") or a hybrid disc with HFS ("no +") as one of the filesystems.

Catalina dropped all support for HFS ("no +"). It and all versions since will reported reject any optical disc that has the old Mac HFS ("no +") filesystem on it, even if that disc is a hybrid disc with a parallel "PC" filesystem which the Mac could theoretically read.

But according to to Wikipedia (perhaps not the most reliable source), Apple dropped all support for formatting and writing HFS ("no +") discs in Mac OS X 10.6 ("Snow Leopard"). A MacBook Pro is by definition an Intel-based machine, and there are only two versions of Mac OS X that are older than Snow Leopard, but that can run on Intel-based Macs. Tiger and Leopard.

The OP says that they burned the DVD on the same MacBook Pro that is now refusing to mount it. A spot-check of MacTracker suggests that any MacBook Pro new enough to be running High Sierra (as indicated in the OP's tag line) cannot be old enough to be capable of running either Tiger or Snow Leopard, and therefore would not have burned the DVD using the HFS ("no +") filesystem.

In Disk Utility, does say what format it is?

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