iPlayer isn’t an ‘open’ service- you have to use a supported client, even if that client is a web browser. Your options are limited to platforms that can support those clients. Personally I’ve found Roku preferable to Chromecast, firestick, full PC. I may at some point have tried to get iPlayer running with Kodi back in the day, when it was XBMC, but XBMC was pretty clunky anyway, let alone on raspberry pi.