I'm trying to reply seriously to this question, because the answer is not so obvious. First of all, Marcel Jacobs was a long jumper with good sprint abilities until 2019, when he was one of the favourites to win euro indoors and he fouled three times in the qualifying round.
Since he was destroyed by injuries, he and his coach decided to give the sprint a go, chasing the world standard and the world champs in Doha, where the goal was to go to the semifinal and run as close as possible to the 10 second barrier. As a long jumper, he didn't have yet the strength and the power required to sprint, which he built in the next fall. He did ran 10.03 in 2019, and 10.10 in 2020 at the italian championships while considering slowing down once he understood he was winning by a large margin. He had a solid season in 2020, where he became more costant and had a shot to break 10, that he just didn't crack. I think is possible to say that probably in 2020 he was in 9.97-9.99 shape, but he ran just 10.10.
What happened in 2021 is that he got way faster in the 60 meters, destroying his 6.63 PR to go to 6.47 winning the Euro Indoors. He got way better at starting, and his technique improved a lot.
With a good season under belt, he was ready to go to the final in Tokyo, that was his ambition. The 9.80 and the win still shocks me to this day.
A very good sprint coach told me that a key to sprinting performance are overspeed workouts, which are basically sprints where the athlete goes over his maximal speed. How do you do that? With a strong tailwind, with altitude, with doping or with whatever technological stuff you can find. The italian federation in 2020 developed this aerodinamic shield, which basically is a sort of tunnel mounted behind a car in which the runner can run without having the attrition from the air. This allows to run significantly faster than normal. One thing that this coach told me is that if your body can run for example 9.85 with +3.0 m/s wind, with the work the body can arrive to do that without the help of the wind, because the body already managed to move that fast, and the body remebers
What Jacobs did was exaclty that with the aerodinamic shield. This coach also told me that the advantages of using this helps are irreversible. The example is Justin Gatlin. He ran crazy fast under PED, and then he returned to those fast times clean. Why? Because the body remebered how to move that fast, and through hard work he could return to those times, beacuse he already ran them. The problem is that if your body is not able to handle this overload, you will be injured. And that's not necessary due to doping. What happened with Jacobs in my opinion is that in the winter and erly spring of 2022, when he was the best version of himself, they worked a lot on overspeed and they tried to run the 100 meters with one step less. Jacobs was flying in training.
According to all sources, he went to Nairobi to run 9.7x. However, something went wrong in Kenya. Jacobs got sick, and he wasn't able to recover. The work done was probably too much to handle, and he barely maneged to win the european title while running through injuries. And he's never been healthy at 100% since then. His body is not ready to handle those training session to run 9.7 or even world record pace, even if he already did so in training with helps. And I think this is the reason why he is always injured. Another thing to notice is that the other documented italian athletes users of this aerodinamic shield are Gaia Sabbatini, a 1500 meter runner, Davide Re, a 400 meter runner, and Alessandro Sibilio, a 400 hurdler. All three of them suffered a lot of injuries in the past two years, even if now they are healthy and ready to go at worlds champs.
I want to believe that Jacobs is clean, but I understand he is suspicious to say the least. This is a possible explanation of his injuires, but along the aerodinamic shield he could have use PED. As an Italian, I hope he is clean, but I cannot be sure about that.