Reaper1337
Senior Member
Despite what Reaper1337 said, all ROMs are based on the stock Note 8 firmware, which means all the included SPen functions and features are intact and working. You can't flash S9 ROMs to the Note 8 and I'm not aware of any ROMs that were directly ported from the S9, thereby removing SPen features. All ROMs that are "S9 ports" just bring certain apps and things from the S9 over while still keeping the base Note 8 features intact.
In short: all ROMs will work like the stock firmware, with the exception of the one project which's name I forgot that's essentially stock Android. But it's incompletely and terribly unstable and buggy, so I wouldn't suggest that anyway.
There can be ports of s9, but there aren't
I talked in general
There is lineageos, which doesn't have spen compatibility