TikTok (know for very short, snappy videos among other things) is a good fit for the brief, almost contentless snippets that pass for the first officially released Eurovision footage, even setting aside the aspiration to target younger people.
In relation the first rehearsals, its possible that what ends up happening is that while the press at large won't see first rehearsals but a very select group of trusted representatives of the press are invited to private screenings to give feedback in private. There is certainly precedent for that in how some have been selected to participate in internal selection processes to give feedback on submissions. (As in those cases, there remain issues about how representative said people are of how the general public responds).
That approach would let delegations would want more feedback when it is easier to change things to get that feedback, whilst avoiding less constructive comments or footage being leaked which could lead to the aforementioned or be against any media strategy/promotional strategy in place. Especially as no feedback at all will only delay the negativity with less of an opportunity to improve the staging.