Not only Forza GT should split up in Featured Multiplayer. But Free Play and Private Multiplayer should also have a Forza GT division split-up.
Here are the following cars and their Forza GT split up divisions for Free Play and Private Multiplayer:
Forza GT2:
2018 Aston Martin Vantage GTE
2017 BMW M6 GTLM
2018 BMW M8 GTE
2014 Chevrolet Corvette C7.R
2020 Chevrolet Corvette C8.R
2014 Dodge Viper GTS-R
2019 Ferrari 488 GTE
2016 Ford GT Le Mans
2015 Porsche 991 RSR
2017 Porsche 911 RSR
Forza GT3:
2018 Acura NSX GT3
2017 Aston Martin V12 Vantage GT3
2018 Audi R8 LMS GT3
2014 Bentley Continental GT3
2015 Cadillac ATS-V.R
2011 Ferrari 458 Italia GTC
2017 Ferrari 488 Challenge
2015 Lamborghini Huracan LP620-2 Super Trofeo
2018 Lamborghini Huracan Super Trofeo Evo
2020 Lexus RC F GT3
2019 McLaren 720S GT3
2018 Mercedes-AMG GT3
2018 Porsche 911 GT3 R
2019 Porsche 935
Forza GT4:
2016 Audi TT RS
2019 Ginetta G55 GT4
2018 KTM X-Bow GT4
Forza TA:
2018 Cadillac TA CTS-V
2018 Chevrolet TA Corvette
2018 Ford TA Mustang
2019 Dodge TA Challenger
Modern Factory Racecars:
2020 KTM X-Bow GT2
2020 Lamborghini Essenza SCV12
V8 Supercars:
2017 Ford Falcon FG X
2017 Holden VF Commodore
2017 Nissan Altima Racecar
(TO BE UPDATED)