My iMac is not registering the Magic Mouse clicks accurately

Thanks, but I understand how it works, I've been using Macs for about 30 years. What I'm saying is that as I click, either something beneath where I'm at, pops up, and gets clicked instead. Or the cursor is directly on one thing, but when I click it, something below it opens. This only began happening in the last month or so, and has been driving me crazy. I replaced my "magic mouse", thinking the issue was in the mouse, but then realized it's beyond that, as both the new one, and a couple other misc. mice I have, all have been having the same things happen.

Another related issue, but maybe not directly, but just as maddening, is that when I try to open a new tab, and click the + button, in the toolbar, instead of opening a tab, it instead shows me a dropdown list of previously closed tabs! It will keep doing this, as I click it over & over again, usually taking about half a dozen times, before it finally just opens a new tab! The same thing happens, when I click on the backspace arrow, in the toolbar. I click it, and instead of just taking me to the previously opened tab, it shows a dropdown menu with a list of all recently closed tabs! This is quite frustrating and time consuming, and is not supposed to do that, unless I just put the cursor on it, not when I click it.. Any ideas?

Yes, it's Safari, but only the aspects of instead of opening a new tab, it shows me a list of recently closed ones, and when I hit the back arrow, it does the same, shows a menu of previous tabs I'd been on, and sometimes even does that when I try to open and app from the Dock! It will show a drop-down menu, of either open tabs, or emails, or other relevant aspects to whatever the app is. It's pretty crazy, I hover over the new tab button, it says "New Tab", but when I click it, the menu pops open of previously opened ones! As I said, it can take me anywhere from three to ten clicks before finally a new tab opens!

I've run MalwareBytes on my system, and just did again now, and it shows nothing. I've run EtreCheck before, but I'll run it now, and see if it picks up anything. Now, Safari has always been rather jinky when it's used with Facebook, for years. It just won't work right, sometimes threads don't open, or pictures, etc. With this last update, 18.1.1, it works with FB as best it ever has, except for the constant opening all kinds of things I don't want. I'll click an emoji, but the person's name will pop up, who's comment is underneath!

Sometimes it'll open their Messenger, as if I want to message them, sometimes it shows I requested friending them, neither of which I did. It will sometimes open someone's profile page, taking me completely off the of the window I was in, and trying to respond to someone's post. It's maddening.... Now why Apple's own browser has always been one the buggiest of all that I've used, I have no idea, as it shouldn't be, at all! I only cautiously try using it, after new updates, hoping some of it's quirks have been addressed...

I don't have a left & right click, on my mouse. To right click, I use control-click. So if I control-click the + button, it will show the menu, as you say it will, when right-clicked. However, when I just click on it, (in effect, left-clicking), it will 80/90% of the time, also open the menu, and 10-20% of the time, it will actually just open a new tab.

And the fact that none of the seven Macs you have don't do this, means about as much as the fact that none of the other 8 -10 Macs I've had over the years, did, or do this either. It's just been an issue with the newer versions of Safari, on this iMac.

I have an apple mouse, and it has no left and right click unless you select that as a feature, which I haven't.

And how would that explain why clicking on the new tab button sometimes, or finally, will actually open a new tab?

The same happens with clicking on App icons in the dock, or the backspace button in the toolbar, instead of doing what they are supposed to do, I get dropdown menus. And this happens no matter which mouse I use, so it's a bug in Safari &/or the entire OS. For when I might control-click to zoom the screen, soon as it gets larger, it stalls, I get the spinning globe, and it will usually jump back to it's pre-zoomed size. And sometimes the scrolling bars disappear, despite my having selected "always show". Many of these things have been happening for quite some time, but it does seem, that whenever I try using Safari, it always gets worse, which is the opposite of what one would expect, due to its "seamless integration", which never quite is achieved.

Oh, and if I'm scrolling down a page, if I hit the bottom, it will suddenly disappear, and a completely different tab opens! I noticed that tab had somehow found its way to the far left position of my tab bar, and is there on every single open window! How it got there I don't know, how I can get rid of it, I don't know, and why scrolling to the bottom of a window should do anything at all like this, I don't know. I do know, I'll have to try my luck with Apple support via telephone, another crapshoot, as I sometimes end up with some who know less than I do....

It's a new Apple Magic Mouse, and even when I set the secondary click to the right, when I click on the open new tab plus sign, whether I use my left or right click, both open the window showing past tabs!