it sounded like it was exactly like some melfest entries in the semifinal in that the prerecorded vocals were kind of the whole thing, but who knows
I based my guess on a few parts of the video, apart from the vocals just generally sounding different to the studio version. Note at 2:17, for example, that Mikolas stops singing and misses a few words towards the end of the line, and while you can still hear some backing vocals, the volume and effects aren't the same as what we're hearing from Mikolas' main vocal track. For the rap section immediately after that, you can hear what sounds like essentially the same thing overlaying itself with an echo effect - so I assume that's Mikolas, and then a backing track of the main vocal part at the same volume, being marginally out of time with each other. The point here being that there's certainly a backing, but you can still hear the live track, and it doesn't sound actively bad. This sort of thing then repeats throughout the performance.
Plus, there seems to be a very clear divide between the backings - which are just taken straight from the studio track, when they're audible - and the main vocals that I assume are live, which are filled with little breaths and minor bum notes and timing differences from the studio version. If there's no live singing going on here, then they've gone to a lot of effort to try and disguise it, which seems like it'd be excessive and counterproductive in the long run.
I'm not saying that everything's perfect here - perhaps they added the backing track because Mikolas has trouble keeping at the right volume and vocal strength on some lines live - but it does feel like we can hear
some live elements here, what we can tell is decent, and the parts using backings can probably be quite easily replicated on the Eurovision stage by getting another vocalist to sing them behind Mikolas live.