@ Edelgard von Rhein: HIP 63835 has four primary stars, and Nerwan's linked system has less than eight too. The other stars in those systems orbit the primary stars. It's easy enough to tell how many primaries a given system has: they all show up on the galaxy map, and will be named as letters. For example, HIP 63835 A, B, C, D. Stars which are in orbit of the primaries are hidden on the galaxy map until you actually visit the system. If you look up Allitnil's posted system, Bloents AY-F d12-0, you'll notice that all eight stars are listed there.
Personally, based on the interview mentioned before, I find it likely that FDev haven't coded in a cap for the maximum number of primary stars into Stellar Forge, but they ran some queries and it turned out that the highest the Forge has produced was eight. Do note that there are two class T dwarfs in the system there, and it's only a mass code D system. It's probably a very lucky configuration, as more massive stars and/or closer orbits would have ended up with some stars swallowing smaller ones.