from various news sources, looks like

1) August 1st onwards, ALL customers flying on Emirates require negative COVID-19 PCR test (done within 96 hours of departure)
2) August 1st onwards, certain customers flying on Emirates from high-risk countries, will be subject to a (second) PCR test upon arrival at Dubai airport

for (2), does anyone know how long the test takes at Dubai airport? wonder how long it'll take (and tight the layovers/transits can be)

assuming flight leaves from a high-risk country, all passengers would be subject to the arrival test (even if DXB if final destination, or transiting)

Edit: after rereading, looks like (2) applies if Dubai is final destination, not for transiting passengers?