Recommended Mirroring App?

Hi there,

Looking to mirror my senior parent's S20+ screen to my S23 Ultra...
(Done with consent of course and intended to view things such as one-time identification sms codes or assist in reading/composing emails, or helping to search missing things on the phone, etc)

Preferably a free/open-source/tried-and-true software - can anyone advise?

Thanks in advance,
Alex