will mac OS Catalina eventually be compatible with my iMac computer 27 inch Mid-2011?

No.

a) To my knowledge Apple has never extended official MacOS support to older models that were previously listed as incompatible.

b) Apple is transitioning to Metal and has announced plans to phase out OpenGL. 2011 and older iMacs do not have a Metal capable GPU.

No. The 2011 iMac does not have compatible graphics hardware to run Catalina and it can't be upgraded to do so.