I reverted back to mIRC v7.64 as I am happy with old mIRC theme (or whatever you call it). Again I find "Windows 10 Aero theme support.." very annoying and uncomfortable to my eyes as shown in the image I posted. Please also keep in mind that I do use the default/standard Theme settings on Windows10 and my OS is updated. I tried to change the Theme settings on Windows10 but that has no effect on mIRC anyway.
I really hope you can find a fix for this issue in the next update, like maybe providing a Theme options in mIRC which can let users to switch between the mIRC Theme used in the older versions as shown here in v.7.64
https://ibb.co/2yMYQ97 and what ever Theme you want.
Thanks for you quick response.