Have You changed any settings in CSM under boot menu? For example if inside CSM You changed Boot from Storage Devices from [Legacy] to [UEFI only] then You can access IRST inside UEFI - navigate further to the right from Boot section. Also make sure Option ROM Messages is set to [Force BIOS] instead [Keep Current].
I set CSM storage devices to UEFI and Option ROM to Force BIOS. I still cant access it from inside BIOS or via Ctrl+I. I tried those previously, but tried again anyways.