Maintaining support for Windows XP is difficult work. It is also far more limiting - more and more libraries require newer versions of Windows, SDKs, C/C++, etc. and Microsoft's support for compiling applications for Windows XP stopped at Visual Studio 2017. Currently, I am having to apply my own patches to some libraries to maintain XP support. This is not really practical long-term and so far I have been lucky that patches have been small and straightforward. The moment one of the libraries mIRC currently uses, which were chosen specifically because they can be compiled for XP, become too difficult to patch, or stop supporting XP entirely, it is likely that mIRC's XP support will also need to end. XP support is also limiting my use of useful, modern libraries that would support newer features. On the other hand, mIRC still working on XP just feels satisfyingly retro ;-)