Correct, Note 9 does not have the hardware for 5G. Even the S10's that are shipping now do not support 5G. Only the S10 5G edition (releasing a little later) will support 5G.5g is the upcoming cellular technology, 5 gHz is an existing WiFi technology that your device already supports so no update is needed.
For the Note 9 to support the upcoming 5g cellular it would need the hardware to support that, we'd certainly have heard if that was included in the original build. Certainly that Samsung is releasing an S10 specifically for 5G support is an indication the Note 9 wouldn't support it with a simple software update.
It is way too early for 5G purchases in my opinion