Necro thread, but this is what came up as I search for the exact same issue I'm having here today Novermber of 2022, running MiRC 7.71 on a 4k display laptop. Pretty small icons, looks almost identical to your image.
I've been dealing with these super small icons for farrrrrrrr too long. I also had found this setting and it doesn't help whatsover. It might be 1px bigger.
Now we are in 2022.... how is this not a major issue at this juncture and "fixed" for Windows 10/11 etc?!?!?
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https://tinypic.host/i/mircdinky.9vry8[/img]