Yes, anytime you're extending a WiFi signal, you're essentially cutting your speeds in half because WiFi can only run half-duplex as opposed to full-duplex like wired ethernet.

Duplex means you can send signal in both directions. Full duplex means you can send signal in both directions at the same time. Half duplex means you can only send in one direction at a time. Simplex means it can only go one direction and you need two cables to do both directions (a lot of fiber-optic connections are simplex with two cables, one for each direction of signal. Light can't really go two directions at once.).

If you add more repeaters, it literally keeps "repeating" the data sent back and forth, slowing down the WiFi because it has to repeat the same data more and more and more, as you add more repeaters.

Source: Took a WiFi class when I was getting my network admin degree. You're never supposed to have more than one WiFi repeater for this reason. Mesh networks are different.

https://www.geeksforgeeks.org/difference-between-simplex-half-duplex-and-full-duplex-transmission-modes/#

There are ways to do it that do not cut the rate in half, e.g. dedicating one band to the internet connection and one band to your client connections, using two routers (one as client, one as AP).