Qolsys panel 4

Hello I have an old original iq panel I want to upgrade to a new iq panel 4 , will the old sensors work? They are from around 2016, also would the old iq sensors be encrypted, and do they need to be? Thx

If you have the original IQ Panel, not the IQ Panel 2, then no, you would not have encrypted sensors. They would be standard 319.5Mhz models.

Those would still be compatible with the IQ Panel 4, they do not need to be S-line models.

Should they be upgraded to encrypted sensors?

Objectively encryption provides security benefits over the older sensors, but there is no immediate necessity to do so. You can replace them now, replace them over time, etc.