Export favorites for update_all
update_all can be told to download only the cores you choose, via its
download filters↗.
Filters select whole cores: a starred game exports the core it runs on,
and every game that core runs comes along with it.
Heads up: a filter listing wanted cores is a whitelist.
update_all will download only those cores (plus MiSTer system files) from
that database and skip everything else in it.