Do you try Archicad library chairs ? Or these : https://bimcomponents.com/Search/chairs#
Importing a model from outside and transform into a gsm object is not an optimized process because Archicad will translate a modelisation into different scripts (heavier than native object).
I invite you to consider the principle of library objects for European BIM design software (Allplan, VectorWorks, Archicad) : very light and extremely parametric objects, much more than an RFA file. A gsm or a lcf file are even more than modelisations. Your workflow will be better with native Archicad object.
Christophe - FRANCE
Archicad Designer and Teacher
Archicad 15 to 26 FRA FULL
OS 11.6 Big Sur - MacBook Pro 2015 - 16Go RAM"Quality is never an accident ; it's always the result of an intelligent effort" John Ruskin