It is very important to note that FireMonkey (FMX) and Visual Component Library (VCL) are two different platforms that are apparently not compatible with each other and they should not be used together in the same module. It means that a module should be using only one of the two aforementioned platforms exclusively. According to embarcadero, the incompatibility of the two platforms is caused by framework differences.
In this Learn Delphi Video, Alister Christie will demonstrate these differences specifically with the TCheckbox. A TCheckBox component presents options for the user. The user can check the box to select the option, or uncheck it to deselect the option. The video above will show us the differences in the OnClick behavior between the VCL and the FireMonkey platforms. Feel free to watch the video above to learn more.