This is a bit surprising to me as I don't think Jacquelin has the engine for pro cycling. His ski speed is excellent but he has a tendency to fade hard over longer distances. Maybe in part that's because he goes too hard too early, but not a great sign regardless.
On paper a biathlete should have an athletic profile similar to someone in cyclocross: lots of 30s climbs in a race lasting between 25 and 50 minutes. Obviously carrying more upper body muscle mass, though. The press release sees a future in sprinting – maybe hardy sprinter, then?
The thing is, Jacquelin
used to be a very smart racer, when he won a world title in Antholz back in 2020 it was by conserving energy and surprising Johannes Thingnes Bø - unquestionably the best skier in biathlon at the time - on the final lap. He also tends to perform well at altitude, which augurs well. Then, at some point, he started taking tactical advice from Simon "go 100% from the gun and collapse on the last lap" Fourcade and although he's become highly entertaining as an agent of chaos as a result, it has led to this current tendency to fade hard. Doing another endurance sport where he has a different set of variables to think about may be beneficial to his biathlon as well as a result.
On paper that might be the athletic profile a biathlete should have, but the examples that we do have of cycling biathletes tend to better fit a full-on GC guy. The two ex-biathletes I can point to are Benjamí Prades, who raced on the IBU Cup back in the mid-2000s before turning his hand to cycling when his younger brother Eduard turned pro - he's mostly been an Asia Tour guy, being based out of Japan for the best part of 15 years, but he's very much a GC climber/puncheur kind of guy, with prominent wins on things like Ijen Crater (13k @ 9,4%), Ayvagediği (5k @ 11%) and the Sembalun Caldera in Indonesia, and always being among the top guys on the Mount Fuji hillclimb. And the other, much better known one, would be of course Florian Lipowitz, whose brother Philipp is still competing in biathlon, being on the IBU Cup as recently as December, although struggling to do enough to break through into the highest level (and frankly at this stage, there's a good chance he never does). Florian was a youth/junior competitor on the Deutschlandpokal and the Alpencup but never made it to the Junior World Championships and obviously was more adept at cycling so focused on that. But it does mean that the two pro cyclists I can name who were verifiably biathletes were actually both GC type riders.
However, Jacquelin is physically larger than either of them, so it may be that the longer climbs are not within his remit, but punchy ones should be. The biggest issue with this kind of late start is as always going to be pack skills, as I can't imagine him enjoying close proximity racing against people who have been riding in pélotons for years. As such, sprinting type activities seems far-fetched as even if he has the physical skillset for it, the ability to surf the wheels, fight for space at speed etc. that sprinters need is likely to be a challenge for a newcomer to pack racing, so I'd think he will be better served as a stagehunter in lumpy races where he can use explosivity at the end of races in small groups.
Miriam Gössner's adventures and misadventures on the mountain bike are probably worthy of mention as well - she was once 5th in the German national MTB championships in the cross-country eliminator, and her love of mountain biking did more or less cost her her career, after her spinal injury and then the race to return before she was physically ready because of the impending Olympics; while she did get back to the World Cup and even scored a later-career podium, she was never the same athlete, with the same insane, peerless speed she'd shown beforehand. It did work out for her indirectly though, as it was where she was posted while convalescing from that injury that she got to know alpine skier Felix Neureuther who was also rehabbing a serious injury at the time, with the two now being married with kids and happily retired together. Elsewise, Lisa Vittozzi is a very strong recreational cyclist and in fact she was the rider sent out to scout new potential Giro climbs in the Sappada region a few years ago, rather than any pro or ex-pro; Lena Repinc won a Slovene mountain Gran Fondo without even training for it, as she competed only as a last-minute replacement for a friend who couldn't ride (she is absolutely tiny and in danger of being blown away in the range in particularly windy conditions, so she's probably well built for cycling), and obviously Romain Bardet and Nans Peters have their connections to biathletes as friends. Former Belarusian champion Stanislau Bazhkou is married to biathlete Hanna Sola and in fact cycled all the way from Minsk to Antholz to surprise her at the World Cup a few years ago. Quentin Fillon Maillet's brother Boris was a useful amateur cyclist, and Ingrid Landmark Tandrevold's brother Halvor rode in the Norwegian domestic péloton in the 2010s.