I already submitted my strange compilation issue and sent a sample. You could compile my component, hence it seems to be that either in my computer setup something is missing, or in yours something is present, that is preventing me from compiling it correctly.
To clarify, in the past I used TMS webcore for VSC but since I updated my delphi version I switched completely to Delphi 12.0. My question was regarding the Delphi Web Designer mode in WebCore.
Regarding the Web Designer question itself, in some other thread you replied to me that for using custom components with the TMS Web Core Delphi IDE Web Designer, I would have to do the components compilation in a different way as compared with the Delphi form designer. The latter requires both IDE stub and the pas2js component source. VSC only required one source. (That is why I mentally associated when I created and used my components in VSC and had it working in the VSC form designer palette)
BTW I have not tried to install the partner components, like the QR code. Will test them this weekend.
Back to my components, I found a way to "inject" (at runtime) the extra properties I need, so instead of using custom components I will inject properties in that manner. Currently am modifying my projects for that method instead, so I can update my WebCore version.