For osnovu themes using underscores.me
ACF do not use, because I prefer to make the configuration settings for the templates and General website settings made in the files.
For this use carbonfields.net
it is free, but it has everything you need, see the documentation and the section on wp-kama(it is the old version, but the part is still relevant).
He's not as popular, but copes with its task perfectly.
Perhaps it has its drawbacks, but for small sites is great.
As a second option, you can use a Meta Box, but for some pieces it will have to pay.
For example, the General site settings page is created with the help of the paid add-ons plugin