I have two sentences.
The cars underwent a rapid change from the application of mechanical technology to digital, that currently takes advantage of
artificial intelligence. Currently, they have become large.
Can I say: Currently, the ones have become large?
No, you can’t really say that.
“The ones” would be used in a situation where you are identifying some subset:
- The ones in the corner
- the ones with a sign on the windshield
- the ones that have autopilot
- the red ones
You need to supply some distinguishing feature that allows us to identify which “ones” you are talking about; if you are talking about all of them, the all-inclusive “they” is appropriate.