Right. I have seen your video and I believe I have an answer for you. Your audio settings are taxing your C.P.U. doing the Analogue to digital conversion while running everything else on the cpu - studio one, tracks, instruments, eFx, buses etc, and whatever is in the background, after operating system and drivers. Those USB-C headphones (you don't mention the model) probably have a digital/analogue converter and amplifier in them. This relieves the cpu of the conversion work. The reason you get better performance when the audio interface is plugged in because of the same reason - the interface is handling all the conversion from digital to analogue and vice versa. Using the interface isn't really a workaround at all - it's actually the preferred method because of this reason. It relieves your cpu of the conversion process because that's what is intended to do. If you insist on running without the interface then you will need to adjust settings like block size, sample rate, shut down all background processes etc. Essentially making compromises. My advice - use the interface at all times and get a decent set of headphones with a proper 6.3mm/ 1/4" jack to plug into your interface for monitoring.