This major release went fairly smoothly, there are 2 post-migration steps which
are listed on the release notes:

    https://github.com/Chocobozzz/PeerTube/releases/tag/v4.0.0

However, you need to do the second part first, adding additional config options
and/or changing the old ones. When you try to run the data migration, it'll
error out telling you which one you need to deal with, so that will help to guide.

Here's what I did:

abra app run tv.lumbung.space app bash
apt update && apt install vim
vi /config/production.yml # change options

Then, in another shell:

abra app run --user peertube tv.lumbung.space app bash

export NODE_CONFIG_DIR=/config
export NODE_ENV=production
export PEERTUBE_DB_PASSWORD=$(cat /run/secrets/db_password)
node dist/scripts/migrations/peertube-4.0.js

After, this I ran a restart of the app service, and things went fine.

abra app restart tv.lumbung.space app