Resize partition without reflashing

I’d like to resize the root partition so I can have / under overlayfs and read-only, and /home writable.
I did a bootable usb stick to use gparted to resize the partition, but I can’t see the extlinux boot prompt at the start.
Can someone help me?
Thank you very much.

You might find this of interest:

Beware that rootfs will need to be found on “/dev/mmcblk0p1”. In part this is because variables in U-Boot are looking in “/boot/extlinux/extlinux.conf” for boot configuration. I have not tried to do what you are trying to do, but I’ve always thought it would be nice to separate out the “/boot” partition from the rootfs. One trouble there is that the flash configuration may also refer to one of the many other GPT partitions numerically or by label…if your changes add a new partition prior to one of the pre-existing partitions, then anything naming those by partition number will fail (those named by label will succeed…rootfs is named by number, and any partition insert prior to another partition will shift the number by one).

You will probably want to get your serial console and stop in the U-Boot prompt, then explore the defined variables. E.g., “help”, “printenv”, “echo $bootcmd_mmc0”, “echo $mmc_boot”, “echo $scan_dev_for_boot_part”.

Thank you very much for your answer.
Do I have to buy a ttl to usb cable to get the serial console?

You may find details about such adapter and how to connect it here.