Comment by any1

Yes, in fact, the protocol states that the client can queue up multiple requests. The purpose of this is to fill up the gap created by the RTT. It is actually quite elegant in its simplicity.

An extension was introduced for continuous updates that allows the server to push frames without receiving requests, so this isn't universally true for all RFB (VNC) software. This is implemented in TigerVNC and noVNC to name a few.

Of course, continuous updates have the buffer-bloat problem that we're all discussing, so they also implemented fairly complex congestion control on top of the whole thing.

Effectively, they just moved the role of congestion control over to the server from the client while making things slightly more complicated.