it's much more than 1 in 2^90. this specific 45 base sequence was found by random search which strongly implies that the odds of finding such a protein are much much higher (i.e. >2^-30) since the experiment probably only searched a couple million proteins

(these are not proteins, these are RNA sequences)

And it's likely that there are even smaller replicators but probably not much smaller. And there are likely more configurations among these 45 base-combinations that can self-replicate. It's also more likely that the first replicators were arrangements of multiple smaller molecules that can amplify themselves, and not just one large molecule.

But even this longer sequence is well within the realm of synthesis by pure chance. RNA molecules can grow base-by-base, so a random walk model should eventually produce it.