All my videos when syncing from iPhone 8 to MacOSX Catalina is showing 1 Jan 1970 timestamp

Hmm.

The Mac defines a date and time as the number of seconds since a base 'epoch' date/time. For Unix which does the same the base epoch is 1 January 1970 00:00:00 GMT. The Mac uses 1904 rather than 1970 although some Mac software uses 2001 and Unix software on the Mac 1970.

See - https://en.wikipedia.org/wiki/Epoch_(computing)

(The Mac operating system is actually based on top of a variety of Unix called FreeBSD.)

It therefore looks like this might be your local timezone equivalent i.e. ten hours difference to GMT.

I do myself see therefore that when a new file is created it will in the Finder sometimes if you catch it, briefly show as say 1970 and then when the file is finished being saved/copied the Finder will normally update it to the correct value. That is the file is initially created with a blank i.e. 00000000 value and then updated to the correct value.

If hypothetically it is failing to update it or more likely is reading the source file and not finding a value and therefore leaving it as zero seconds since 1/1/1970 then this might explain matters to some extent.