What is the best free adblocker for Safari on my iMac?

We've been using K-Block! on all of our devices for at least a few years now. It's free and available on the App Store. The ratings on it aren't as high as they used to be, but I compared some of the "best" ones against it a few weeks ago, and none of them did any better. A couple were actually worse.

Or, use the Brave browser. It's built on the same base code as Chrome, but with none of Google's invasive data collection services. Brave is also designed to keep your web browsing private. And, best of all, it has ad blocking built in, which works very, very well. When you use a typical ad blocker, many sites will block you from accessing the site until you turn it off. With Brave, most of them miss the ads are being blocked because there's no third party plugin to detect.

Vivaldi browser based on Chromium has a built-in ad blocker....at least a partial one. I try not to block ads unless they are interfering with the page or really slowing the browser....this gives me easy control to block trackers only or block both ads & trackers. Vivaldi automatically blocks the really dangerous ads IIRC. Having it built-in is much less risky since it is hard to keep track of browser extensions....one day they are great, but the next day they may be no longer being developed by the same developer....I try to minimize the amount of third party software I have installed.

https://vivaldi.com/features/ad-blocker/

In addition to the other excellent comments, and a bit of a different tact, I suggest that you consider an overall network ad-blocker, like either Pi-hole or AdGuard Home. Both are free.

FWIW, I host Pi-hole on a Raspberry Pi 0 2W. As such, any of my network devices, computers, tablets, phones, etc. can have ad-blocking enabled. I find this advantageous when you have limited Internet bandwidth. I typically see between 20-30% of the overall traffic, which is ad-related, blocked.

Yes, Ka-Block!. Didn't notice I missed typing the a.

Don't know what you mean by "WITHIN the AppStore". If you mean finding a particular type of app, there is a search bar.

Privacy and ads are two entirely different things. Protecting your privacy means not doing things that a browser like Chrome does by default. Such as tracking your browsing habits, and even your computer usage. Ads are just ads. No different than the ads that run during a TV show. The advertiser has no idea who, or how many people are watching.

Did you mean "Ka-Block"? No "K-Block in App Store.

It would be helpful if these better options were made known WITHIN the AppStore.

Eve4n after the recent AppStore purge it's a crapshoot of apps that rarely show high numbers of downloads/reviews (why is this BTW)?

Why it gotta be such a mind melt when Safari claims private browsing always - but now I need an ad-blocker, or a Pi-Hole, or when do I need a VPN? (Note: my initial VPN experience cut off wifi - arghs).

-WHO doesn't want/need safe browsing and untethered access? (seems predatory on ignorance/lack of xyzzy).

-WHY Editor suggestions meager to inform or recommend in general? (but really nothing on ext??)?

-WHAT's the crux (+/-) for best practices on Safari (average & aspiring users)?

+WHERE are these extensions? (Regular search results show few with no/low 0-7 (!) downloads).

I'm interested in opensource.org, but absolutely need seamless access to other ecosystems bc emails/Profiles (which I hate, but necessary (or are they?).

I don't want to be too demanding, but need is a cruel dictator :\

THX!