by Barking Bandicoot.
I too am using the Bitnami docker image - but with Caprover.
To upgrade I needed to follow these instructions - with some adaptations.
https://docs.bitnami.com/aws/apps/moodle/administration/upgrade/
It would seem either way you go some things will be easier and others harder, depending on your server setup and application requirements.
I just upgraded to 4.3.3 - now 4.4 is out! Ugh!