Martijn Zaal : you should have no problems at all,

Easiest way to access priority security is between checkin counters 24/25
You can use the automated gates or have staff open the barrier, just show them your SQ BusinessClass boarding pass.

Afterwards go right towards stairs/lift towards priority security,
Once on the mezzanine,
the right side lane is for priority,
if staff is distracted, just wave them over and show your BP and you can enter

When in the priority queue, don't be surprised if persons are going ahead of you.....
Privium gets priority over priority,
When we departed in July, there was some audible grumble but upon explaination : privium iris scan paid service/betaalde dienst
All was turned to understanding

Be reminded after security, ALL passengers join the queue for passport control.
You only get priority if Privium/Crew/Diplomatic/Impaired~Wheelchair


And thank you for asking about the lounge situation!