Comment by badsectoracula

Lazarus[0] has a Gtk 1.2 backend that i occasionally fix (though it has been a while since i tested it), but you need to install the Gtk 1.2 libraries from source[1] since no current distro aside from Slackware (from where i got the sources and patches) packages it. Even Slackware though doesn't provide gdk_pixbuf (which Lazarus needs) though, so you'd need to compile that.

I'm not sure if GTK1 (the linked one) is backwards and/or binary compatible with Gtk 1.2 though.

[0] https://www.lazarus-ide.org/

[1] http://runtimeterror.com/pages/badsector/gtk12/