Context: To minimize the heath risk during pandemic, many CFIs, especially senior ones, are not comfortable to conduct instructional flights with students in a narrow cabin. In the meantime, many pilots are due soon for flight reviews (BFR), but still within the 24 calendar month valid period.
For the ground portion of the flight review, a remote video call should make no difference with respect to regulation compliance. So the remaining of the question is for the flight portion,
Is it regulation-compliant to let a CFI to endorse me while the CFI is on the ground while I am going solo for the flight? There will be real-time videos, which cover the flight instrument panel, my maneuvers and cockpit outside views, broadcasting to my CFI in real-time, as well as recorded for post-flight verification. The CFI will be able to communicate to me in real-time through a hand-held radio, and will watch my takeoffs and landings near the runway, just like what happens on a first solo.