Technically, a 2019 iMac isn’t too old, because as long as it has enough memory and storage, it still meets the macOS compatibility requirements for Creative Cloud apps. However, at 5 years old it is starting to reach the typical period where a computer can start to feel sluggish because new software tends to be written for the capabilities of newer hardware.
There is one different thing about the last 5 years on the Mac. In 2020, Apple started releasing Apple Silicon Macs, starting with the M1. Those perform so much better that they rapidly made the Intel Macs look a lot worse and less efficient. So during this transition, Intel Macs can seem slower sooner than they would have traditionally.
If the slower performance starts to bother you a lot, and you can’t afford a new computer soon, one way you might restore performance is to roll back Creative Cloud apps to a version where you were happy with the speed. Mac software developers started writing new versions to take advantage the higher capabilities of the much more appealing Apple Silicon Macs, so for example many newer features that benefit from multi-core processing, GPU acceleration, and AI tend to work much better and faster on an Apple Silicon Mac. Running these types of features on an Intel Mac can be disappointing.
Just be aware that the Creative Cloud installer provides only the last two major versions for installation.