Weird. Please answer the following questions:

1. What widgets are those?
2. What is the panel thickness?
3. Does the issue still reproduce if you make your panel absurdly thick, like 150px thick?
4. Do you have any "margins separator" widgets in your Panel--perhaps surrounding those two widgets?
5. Does the issue happen in a new fresh panel, if you add those widgets to it?
 6Does the issue reproduce if you create a new fresh user account and then add those widgets to the panel in that user account, or to a new fresh panel in that user account?

Created attachment 162747 [details]
Panel 150px

1. The trash widget (Right-click on the desktop → Add Widgets… → Choose the trash plasmoid → Move it to the bottom panel).
2. 78.
3. Yes, I attached another screenshot as an attachment in the first post.
4. No.
5. Yes.
6. Yes. Up to a panel thickness of 70, all icons change, but after a thickness of 70, the trash widget icon stops increasing.

Thanks for that info. Now can you attach your ~/.config/kdeglobals file?

Created attachment 162780 [details]
kdeglobals

That's the entire thing?

(In reply to Nate Graham from comment #6)
> That's the entire thing?

Yes, I only found this file.

That's not what I expected at all. You are using KDE Plasma, right? What's the output of the command `find ~ -name kdeglobals` when you run it in a terminal window?

Created attachment 162854 [details]
/home/user/.config/kdeglobals

Thanks. Unfortunately I didn't find the expected config entry in there that I was suspecting caused the problem.

Does Debian ship its own kdeglobals file somewhere on the system that might be overriding it? You could look in /etc/xdg/. If you find one, can you attach that one too? Thanks!

There is no kdeglobals file in this path. Have you tried to reproduce this problem on your system? Are all your icons getting bigger? Am I the only one having this problem?

I have tried to reproduce the problem and could not. I am at a loss to explain what could be causing it.

Did a clean install of the new system but the problem remained. Could it be that I'm using VirtualBox?

Possibly. Or perhaps it's yet another Debian-specific issue. Would be interesting to know if you can reproduce it with a real install, not in a VM. Even trying in a live session would help.

Unfortunately, at the moment I do not have such an opportunity.

Since I'm unable to reproduce this issue in Plasma 6 and no one else seems to be affected, I'm afraid there's not much we can do here. I'm going to mark it as fixed in Plasma 6, but do feel free to re-open the bug report if you upgrade to Plasma 6 in a few months and find that the issue is still present. Then we can re-investigate.