Yeah, this is something many climate advocates say - that it is better to keep the car you have - but I don't think this is backed up by data at all. It's very clear that that EVs are able to save more carbon emissions than in a fairly short period than you would save by not continuing to drive an ICE vehicle, with manufacturing included.
If we were going to have a simple rule, replacing all ICE vehicles today with EVs will be far better for the climate than keeping them.