DDG and Mullvad are private search engines as they strip out your trackable metadata and don’t pass on your IP address.

Is that so? How do you know?

I’m not using it at all, I use the *DAV functionality of my paid mail provider.

I did research on what solution I would use alternatively – with requirements very similar to the ones you proposed – and EteSync checked all the boxes, which is why I recommended it.

I set up an instance once, and it seemed to work just fine, but I haven’t thoroughly evaluated it.

Doesn’t that apply to any search engine?

I’ve been using SearXNG and its predecessor for years and I have no reason to change that. Highly recommend you check it out.

They don’t support DNSSEC.

you need to chill

How about EteSync?