Yanbu If your baby cries a lot in the car, I simply wouldn’t go. How horrific for you all.
If you MUST go, eg to see a dying relative, then yes split the journey over two days. We drove to south of France this way when baby was 11 months. Our baby liked the car but gets fidgety after a while so we stopped for an hour every nap cycle so baby could wriggle, look around, change nappy, have cuddles, feed.
On a six hour trip, I would aim to set off when baby is ready for a nap, then when baby wakes up do your level best to entertain (suggest new toys, books, sing songs, and one adult in back of car with baby). When you spot signs of baby being annoyed, plan to stop, make it a good long stop so baby starts getting tired, then set off again.
I might manage the drive in a day, setting off at 9.30 am and arriving at tea time, but only if baby was happy in the car. Otherwise yes, split the stress of the trip over 2 days.