Native 'Take Screenshot' defective/non-functional on Trisquel 11 (Aramo), as updated via Terminal option.

Could you tell the package's name? I searched for “Take Screenshot” in Synaptic and don't find anything that might be that program (with Trisquel Aramo using MATE desktop).
What I can tell is that default's MATE screenshot program does work as well as before.

@Lugodunos

Apologies, but having said in the OP "now have discovered that the native 'Take Screenshot'" (emphasis on native, as in the default program that came originally with Trisquel 11.0), I'm afraid I cannot tell you about what "package name" means in this case. When I look in 'Add/Remove Applications', the only program I see, when searching for 'screenshot', is the additional one that I installed (with 4 star rating), but only after discovering that the default program, named 'Take Screenshot' (that came with the OS under 'Accessories', as the last/lowest entry in that list), no longer worked for me.

I had previously used the default 'Take Screenshot' quite a few times, so was surprised that, for me anyway, it no longer worked. Given you report that the default MATE screenshot program does "work as well as before", then I can only say that this issue, for me, only appeared after using Terminal to upgrade from Trisquel 10.0 to 11.0.

The original/default MATE 'Take Screenshot' program, for me, works normally, up until I attempt to save the highlighted area I intend to capture. It loads, allows changes to what kind of capture, and even makes the highlighted capture box. But when I press 'Take Screenshot', the program disappears entirely, and doesn't offer to save anything to a chosen location, as it always had before.

I only installed the program called simply 'Screenshot', using Add/Remove Applications, *after* the default MATE 'Take Screenshot' program, in 11.0, failed to work at all.

Apologies for being so verbose. I just want to make certain that is, in fact, the original/default/native 'Take Screenshot' in Trisquel MATE 11.0, with which I am having the issue. So for now, I had to temporarily add the other 'Screenshot' program (as it's called in Add/Remove Applications.)

Thanks kindly!

So, having the make-utils package and the above command line using the screenshot I know, I have mate-screenshot and I tried to reproduce your bug but it worked as it should.
I installed Trisquel Aramo (11) from an ISO image, so I guess the problem effectively came with the up-grade.
After a (not so) quick search, I didn't find any configuration files or such tied to mate-screenshot or mate-utils.
If the above command given by Magic Banana proves that it is mate-screenshot that doesn't work for you, you might consider re-installing the mate-utils package.

@Lugodunos and @Magic Banana;

Thanks so very kindly for your assistance.

In the end, I decided not to try and chase an error (which could've come from anywhere.) Instead, since I try never to save anything important on any Linux OS drive (as I'll never be proficient or expert in chasing down such loose ends), I just decided to copy the browser profile to a different location, and then installed Triskel 11.0, alone, to that isolated Linux drive.

So now 'Spectacle' is the screenshot utility with this KDE/Plasma version, and it's working fine, for now anyway.
I'm hoping that maybe with this method (replace instead of repair), it'll be easier to just reinstall any OS, when anything at all goes awry. Start from scratch, including any LTS upgrades. Going to give it a try anyway.

I really do appreciate your consideration! I'm just never going to have the time (or discipline) to search out the cause of various OS conditions. And must reconcile that, while I'm still *fighting* being held captive to Windows, Mac/iOS, etc., I'm also unable and/or unwilling, to learn the comparative enormous complexity of Linux, and then even still, need to so often lean on the good graces of ALL the generous, like yourselves.

With thanks...

@Hikaru

Yes, there is a 2nd internal HDD for any important data. (Trisquel (now Triskel), is isolated by itself to an SSD and also external device(s), as needed.