No, you can use two algorithms at once (one placed in Program A and the other in Program B, both together referred to as a Performance), either totally separately or in parallel or series. Some algorithms are multi effect (e.g. SpaceTime) which can give you more than two effects at once. Have a look at the Quick Start Guide for the H90, it should make things much clearer.
https://cdn.eventideaudio.com/uploads/2022/11/H90-QRG-141360-Rev-A.pdf
