Getting error when installing postgres with existing /var/lib/postgresql

I want to install postgres (on debian) with an existing data directory at /var/lib/postgresql, but installation gives this error.

Setting up postgresql-13 (13.3-1.pgdg100+1) ...
Configuring already existing cluster (configuration: /etc/postgresql/13/main, data: /var/lib/postgresql/13/main, owner: 106:113)
Error: move_conffile: required configuration file /var/lib/postgresql/13/main/postgresql.conf does not exist
Error: could not create default cluster. Please create it manually with", "", "  pg_createcluster 13 main --start", "", "or a similar command (see 'man pg_createcluster').

I'm provisioning a new system, so I don't want to restore the old /etc/postgresql along with the old /var/lib/postgresql. I want the postgres installation to create it from scratch like on a fresh installation, then my automated provisioning scripts will change the few settings that are different from the defaults. (I shouldn't have to bring along the old /etc/postgresql, since that could be bringing outdated configuration along with it if postgres has changed its defaults. Better to use the latest /etc/postgresql and just change what's needed.)

What's the best way to make it work? I could first install postgres without the old /var/lib/postgresql, then stop postgres, delete the newly created data dir, restore the old data dir, then start postgres. But this is more messy than it could be. Is there a way to force postgres to ignore /var/lib/postgresql and just recreate /etc/postgresql? Or any other options?

I'm surprised it isn't already possible since it's a common use case with cloud providers to attach an existing volume storage (which contains an existing /var/lib/postgresql) to a brand new server (which doesn't contain /etc/postgresql) and install postgres on that server.