Hi Matteo – welcome to the forum!
All of the DIY Packrafts are capable of carrying over 100 kg. I probably wouldn’t use an Ultralight packraft for bikerafting though, as the ultralight fabric is more fragile, but you could do so if you were more careful.
Each DIY Packraft kit comes will scrap fabric to make attachment points and grab loops, and you can place them wherever suits your needs. To figure out where to locate them, I would first build the packraft and then balance the bike on top, with the wheels and everything placed as they would be during paddling, and then mark the locations where tie-downs would be best located to attach directly to the bike’s frame.
You may also want to add an airtight zipper to your packraft so you can store gear inside the tubes, as you will not be able to store as much gear on top of the bow if your bike is there. You will certainly have more room if you choose a larger packraft.
Cheers!