Totally agree with the principle of having some practice to acclimatise yourself to being on camera and become comfortable with it. It is interesting to do this also as it can help you with your body language.
As someone who regularly interviewed and recruited graduates over a thirty year period I can't stress enough just how important body language is in any interview situation. I've seen very well qualified people slouching, crossing their arms, leaning back in their seat etc and it doesn't give off positive vibes.
Unfortunately I don't have experience of online assessment centres, but just bare the above in mind, if cameras are on, you're visible at all times.
Regardless of online or face to face, don't try to be something your not however, just be yourself, relax, grow into it and smash it mate.
Have a few flights in and out of Glasgow already booked for next year, I'll keep a close eye out for the border guard with the name badge Kenny "Fucking" Powers