and if they join the Fediverse, of course they’re going to harvest data from anyone federating with them too.

From the Mastodon blog post about Meta federation:

Will Meta get my data or be able to track me?

Mastodon does not broadcast private data like e-mail or IP address outside of the server your account is hosted on. Our software is built on the reasonable assumption that third party servers cannot be trusted. For example, we cache and reprocess images and videos for you to view, so that the originating server cannot get your IP address, browser name, or time of access. A server you are not signed up with and logged into cannot get your private data or track you across the web. What it can get are your public profile and public posts, which are publicly accessible.

Using Arc on Mac; does the same.

I don't know if it's a plugin I installed or maybe it's default behavior, but if you have the picture icon to the immediate left of the comment counter, you can click on it to expand the photo without having to go into the post.

Alternatively, Kbin Subscriptions Panel

Additionally, the Channel icon in the top right (next to your username) has an option to view only posts from subscribed mags/communities.

Not to the top bar, but here's a side panel option

Additionally, the Channel menu icon (to the left of your username) allows for viewing only posts of subscribed mags/communities.

Complete version of "The Star-Spangled Banner" showing spelling and punctuation

O say can you see, by the dawn's early light,
What so proudly we hail'd at the twilight's last gleaming,
Whose broad stripes and bright stars through the perilous fight
O'er the ramparts we watch'd were so gallantly streaming?
And the rocket's red glare, the bomb bursting in air,
Gave proof through the night that our flag was still there,
O say does that star-spangled banner yet wave
O'er the land of the free and the home of the brave?

On the shore dimly seen through the mists of the deep
Where the foe's haughty host in dread silence reposes,
What is that which the breeze, o'er the towering steep,
As it fitfully blows, half conceals, half discloses?
Now it catches the gleam of the morning's first beam,
In full glory reflected now shines in the stream,
'Tis the star-spangled banner - O long may it wave
O'er the land of the free and the home of the brave!

And where is that band who so vauntingly swore,
That the havoc of war and the battle's confusion
A home and a Country should leave us no more?
Their blood has wash'd out their foul footstep's pollution.
No refuge could save the hireling and slave
From the terror of flight or the gloom of the grave,
And the star-spangled banner in triumph doth wave
O'er the land of the free and the home of the brave.

O thus be it ever when freemen shall stand
Between their lov'd home and the war's desolation!
Blest with vict'ry and peace may the heav'n rescued land
Praise the power that hath made and preserv'd us a nation!
Then conquer we must, when our cause it is just,
And this be our motto - "In God is our trust,"
And the star-spangled banner in triumph shall wave
O'er the land of the free and the home of the brave.

I think this is correct, but I'm not 100% certain...

To defederate from an entire instance, in this case lemmynsfw, click the triangle-looking icon (beneath top bar, towards the right side of the page) and then set Status to Off.

To block just one of the categories of lemmynsfw, on the right side, scroll down just a little to see Magazine, then click the "no" icon for block magazine.

An easy-ish way to explain it is to use the example of email. Gmail, Outlook, Proton, your private email server...they all are independent of each other but can interact with each other. That interaction is "federation". Kbin, Lemmy, and even Mastodon, PeerTube, et al can interact with each other even though they are independent of each other, yet alone not the same "usage" (i.e., link aggregators vs. microblogs vs video hosting...).

Defederation simply means ending the interaction. The instance will still operate as is, but will not interact with what it has defederated from. In the case of Beehaw, they still interact with the rest of the Fediverse, but not with the instances they blocked.

To circle back to the email example, if your private email server defederated from Outlook, you'd still be able to send/receive email from the others, but not Outlook.