So - it's June and X90PP are still rocking March security patches - while Samsung and google are already rolling out June patch...
Security Updates only every 3 months, in the first year. What will it be once X100 is out? Usually vivo software support then takes an instant drop.
And while the X90Pro Funtouch is the only Vivo phone in the Android 14 beta channel, of course X90PP doesn't appear there. 1 or 2 android updates is still the most likely answer to the original question. I guess 2 because Vivo has to improve and a single one is even too little for Chinese users nowadays. I would guess A14 and then a Final update to A16. And security updates dropping to 6 months frequency after 1.5 years. The update to A16 may then well be the second last update the phone receives, with a single security patch update around 6 months later. (or at the 4 year mark)