You can be *as native* as GTK on Linux :)

analognoise · on Oct 21, 2021

GTK is not required on Linux for FreePascal GUIs.

See MSEIde, which is directly X11: https://github.com/mse-org/mseide-msegui

"MSEgui is a complete independent Free Pascal widgetset. It does not use any other widgetsets like GTK2/GTK3/Qt4/Qt5. MSEgui interacts on Unix directly with X11 server (like other widgetsets do). On Windows, it deals with the low level Windows GDI interface."

Although a separate windowing set than Lazarus, both are enabled by the FreePascal compiler.

Lazarus does have a GTK backend as an option on Linux.