I press the accent key and the "e" key simultaneously, several times, however in the mIRC editbox it doesn't always accentuate the words. The same happens with the accent "~" in the letter "a".

When you say you press the accent key, which key is that? Is it a combination of keys?

The language for Windows 10 Pro 2004 (19041.546) is English. The keyboard is a Razer Huntsman PT Black.

I was not able to find a "Razer Huntsman PT Black" online. I was able to find a "Razer Huntsman Black". Does PT mean its Portuguese?

Is your keyboard set to use the Portuguese language?