Tested the attached application with:
- Lazarus 2.0.12/Trunk and FPC 3.2.0
- Windows 10, Linux Mint 19.2 Cinnamon, macOS 10.16 Big Sur
Please do the following:
1. Open then build plugin.lpi from pluginlibrary subfolder. This is the library(dll, so, dylib), it contains form, buttons, images, etc...
2. Open test.lpi, build then run the project. When you press the "Load" button, the form from the library is loaded then embedded in the main form.
Is this what are you after?