When I flew charter business jets we used to brief that either pilot could initiate or call for a reject regardless of PF/PM or PIC status.
When I joined my first airline this changed to the Captain is God principle that only the PIC decides the reject. I still don’t fully agree with that concept.
US based employer so we don’t use or can’t even have ‘low’ time FO’s and at least on a Boeing everything is well within reach of the RH pilot. Spoilers can easily be briefed as an “if I forget then you do it” item and that applies regardless of PF/PM status.
The whole caveat with the PIC-decides model as that the SIC is still expected to execute the reject when the Captain is either incapacitated or otherwise incapable of making the correct decision as a Master warning at 80kts isn’t really the time or place to have a meaningful discussion about the philosophy of Boeing.