NEC3 Option A - if PM fails to reply to contractors design submission within period of reply stated in contract data part 1 (4weeks), can the design be deemed as accepted or is the contractor required to raise an early warning or compensation event.
The only deemed acceptances in NEC3 are to do with the compensation event process where the PM fails to respond to a notified CE, a quote or fails to make their own assessment (and even then only after a formal reminder and a further two week period of no response).
Lack of response to a communication within the timescale is a compensation event. This is especially important for design as the contract also states the Contractor does not proceed until the design (as required in Works Information) has been accepted. Any cost that the delay in design acceptance causes you (if any) will then be recoverable as part of that CE.
But remember to early warn as soon as the time scale is up as otherwise the lack of early warning could reduce the assessment of the compensation event - see clauses 61.5 and 63.5