Getting this sequence by random chance out of a pile of nucleotides is a 1 in 2^90 chance. That's around 1.2*10^27 or just around 20000 moles! Not at all an impossible number.
If primordial earth's oceans had nucleotide concentrations comparable to Bennu, then there would be about 10^39 nucleotides in the ocean.
Nucleobase synthesis in interstellar ices[2019]
https://www.nature.com/articles/s41467-019-12404-1?error=ser...
Chemistry of Abiotic Nucleotide Synthesis[2020]
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.
OP's Gianni et al 2026 paper connects 45 nucleotides, taking 72 days (1700 hours) to yield 0.2%.
The latter effort is like drawing the whole owl.
That is incredible patience. Without access to the full article, I read only the abstract. I wonder if they used simulations to narrow the candidates?
* 99.8% of the starting molecules fail to form the desired product
* The ones that do, form 0.026 bonds per hour