I assume I cannot do it from the Raspberry, correct?
Asking because I’ve formatted one partition with drive-manager and tried to resize using disk utility on MacOS Big Sur but I’m getting an error saying that partitions can’t be resized
If possible go with a GParted Live USB stick and you will have latest version of GParted running
There is as well a Debian apt package available but this was not updated for more than 2 years. See note on GParted download web site https://gparted.org/download.php
Next to this you would need to have a (remote) desktop environment running