The R7 uses Canon’s newer Multi-Function Shoe. It remains electrically compatible with many older Canon-style flash accessories through the standard hot-shoe contacts, so legacy devices like the ST-E3-RT and similar third-party units can often mount and function normally.

The main issue is weather sealing, not basic triggering/communication. The Multi-Function Shoe adds front contacts and has a different shape at the front, so the rubber sealing collar on older weather-sealed accessories was designed for the older shoe and doesn’t fully cover the new front section.

That’s what the AD-E1 adapter does: it adapts the new shoe to the older physical/sealing standard while maintaining a sealed connection. Without the adapter, many older accessories still work, but you lose the weather-sealed interface.

So in short: function is usually fine directly on the R7; the adapter is mainly needed if you want proper sealing with specific older Canon flashes/transmitters/cords that have legacy sealing collars.