Thanks for that. Digging around, here is a list of tested combinations that I posted on the ML circa 2015 plus a couple of recent additions. First column is Lazarus, second is FPC:
0.9.24 2.2.4
0.9.26 2.2.4
0.9.28 2.4.0
0.9.30 2.4.4
1.0.0 2.4.4
1.0.0 2.6.0
1.0.8 2.6.2
1.0.14 2.6.4
1.2.6 2.6.4
1.4.2 3.0.0
1.6.4 3.0.2
1.8.4 3.0.4
Those are for GTK v2, most if not all of those also supported the current version of Qt with varying degrees of reliability. The last that supported GTK v1 was 0.9.24+2.2.4.
MarkMLl