Why is my keyboard typing random letters?

This might be a hardware issue, especially since the letters you're seeing (8, i, k, m) are all in a vertical column on the keyboard. Mechanical keyboards work on a matrix circuit, so if there's a short in a column or row—often due to dust, spills, or some internal damage—it can cause multiple keys to act as if they're being pressed.
Try checking for any debris under the keys or signs of liquid damage. Also, you can reset the firmware using the SteelSeries Engine software—just go to Settings > Device > Apex Pro TKL and look for the reset option.

I had a similar issue, and it turned out to be a faulty switch. Even when I wasn’t pressing it, it sent false signals affecting nearby keys. If cleaning doesn’t work, you might need to check if one of the switches is shorted. Good luck!

If it's dust causing the problem, try turning the keyboard upside down and shaking it gently to dislodge anything stuck inside. Blowing out any dirt can also help. Sometimes, a good cleaning is all it takes to fix these glitches.