Ublock Origin can work this way with a couple of clicks. Use the advanced user option. Allow all content globally, and then use local override on sites where you want ad blocking.

Thanks. Unfortunately it doesn't seem as straightforward (or I'm missing something)

The advanced options documented here (https://github.com/gorhill/uBlock/wiki/Advanced-settings) don't seem to fit the description.

What advanced settings allows is to edit the blocking rules with something like the uMatrix gui. Once advanced is set, open the uBlock dropdown, then click on "requests blocked".

You will see a table with three columns. The second column edits the global rules, the third one is for local rules. Each of the rows in them shows three bars once you hover over one. Green = allow, grey = noop, red = deny. (Noop is the setting to not overrule the adblocker lists.)

In the "all" row at the top, click on green in the global column, to allow everything everywhere. Click the lock icon. Now uBlock won't interfere at all.

On a site where you want to block according to the lists, open the dropdown, and in the row with the site's domain name, click the grey bar in the local column. Click the lock icon to save the setting across sessions. uBlock will apply the lists' rules to that site.

If this is unclear, I can make a guide with images.

AdGuard extension can do this. Check the setting "Invert whitelist" in the "Whitelist" section.

I'm fairly sure you can just use uBlock Origin and just disable all the filters.