He is skipping f3 completely, similar to Verstappen who skipped f2 and Raikkonen who skipped both. Whether Antonelli will make f1 following this obviously depends on his junior career and what happens in the driver market.
I would argue that with the cost cap and the restrictions on testing, it is extremely challenging for young drivers to break through. I’m personally impressed with Sargeant and applaud his resigning for next year. I could easily see him getting dropped however if his results to Albon don’t continue to improve.