Forgot to copy or typo?
I forgot to copy.
I looked into Makefile.Release and realised that instead of
this It was including thisC:\Program Files\MySQL\MySQL Server 8.0\include
I deleted qmake.stash and config.cache and repeated the qmake again and this time I generated qsqlmysql.dll successfully.
Tested it with Sample Cpp code in Qt, it's working.
@Christian-Ehrlicher Thanks for the suggestion.