This is how I manage my punting phone on an iPhone.
It is an eSIM not physical SIM and you need to scan a QR code (barcode) that you get from your mobile phone company to get it to work.
It does work but you need to keep your wits about you.
You will have Primary and Secondary numbers and top right the signal strength indicator is split into 2 horizontally, that is the only outward clue there are 2 numbers.
But, if messages or calls are received then will ring exactly the same (may be able to change it but I haven’t) and messages all appear together. I have my ‘preview’ settings for messages disabled on lock so prying eyes don’t notice anything what I am up to. If any messages received from numbers not stored in my phone then say it was the GP / hospital confirming appointment (I have a few of these) or car park telling me expiring, or EDF harassing me for a smart meter or other nondescript reason that I have committed to memory.
Also, can only use WhatsApp with one number per handset so one of the numbers will not have a WhatsApp.
And both lines have to be with the same network if the phone is locked.
In terms of social media, mine are all liked to ‘me’ and not ‘not me’ so easy enough as don’t have a punting social media persona.
Also, if you and the SP use iMessage then can cause problems - I change the iMessage setting to ‘off’ before sending that first message to force all future ones via message and not iMessage.
And finally, and I know I’ve said it before, keep your wits about you or you could call from the primary and not secondary number.