I used procedural freebasic only. After checked it OOP I would say I'm wrong 
FB has so much IDEs but most of them abandoned, only three keep going: WinFBE, PoseidonFB, VisualFBE. Community efforts is scattered, they never think about joining force to make something like Lazarus. There are many gui libraries only because there is no LCL, most of them are wrapper over winapi or porting existing libraries like gtk3, fltk... FB is more closer to C so generating such bindings is more easier than Pascal. The fact why Free Pascal doesn't have that amount of gui libraries because it has the LCL 
FPC does have them. It had QT,FLTK, wxwidgets, gtk1,gtk2 (and various wrappers like fpgtk) , fpgui, kcl and whatever in the 2000-2005 era. However as soon as LCL was usable on both Linux and Windows, the smaller efforts started to get less popular, but if you search thoroughly you can probably find the headers.
Not all died, fpgui is still somewhat maintained, and also MSEGUI was maintained till the author passed away late last year (and they are still regrouping, too early to tell), and KOL also lasted longer than most, maybe because the latter was also for Delphi.
Like FB gui now, the more serious users of such efforts are often using them for PLC-HMI, POS and other one-application(kiosk) purposes.
Also, LCL using native widgets leaves room for at least one good owner drawn library, so that users have something to choose.
FB OOP style is not my taste. I don't say it not good but simply not my taste. I come from Java/Xtend/Fantom so I used to their OOP. Even Object Pascal I don't like and mostly use procedural programming 
Object Pascal and Java are not that different OO wise, except for the GC of course.