I've seen this addressed before, but honestly I'm not satisified with the answers given years ago.
Why is the canvas view playback so slow? It works relatively well in most other animation programs, even Macromedia Flash 8 Pro, which was my software of choice until a couple of years ago, had basically realtime canvas playback. Most answers say to use the Test Movie function, which works but it's annoying to have to open it every time you want to look at 5 or 10 new frames of character animation to check if the motion is good. Ontop of this if the animation is half a minute, maybe even a couple minutes long this is unneccesary extra time to have to sit through the entire movie. It would have been more acceptable if the jump to CC did not remove the Bandwidth Profiler function in test movies (let you scrub through the timeline of .swf files) and adding actionscript to jump to spots is just unintuitive for artists. My computer specs are Ryzen 7 3800x, RTX 3090, 16gb ram, so I'm confident it's not that.
I guess I just want to know why flash 8 can run things perfectly smooth but the new versions a decade+ later can't. Is GPU rendering just not possible? I hope I'm not coming off overly hostile, it's just frustrating animating for several hours a day, then looking at the final export and it's faster than what you were looking at in canvas view.
I'll add an example of both programs playbacks side by side for even an extremely minimal and simple rough animation.
adobe animate has several starting modes. the two main modes are html5/canvas and actionscript 3.
now, whatever you mean by canvas is not what it means relative to adobe animate since html5/canvas was introduced years ago.
it appears you're asking why playback of actionscript 3 projects within flash 8 vs animate v? is faster. if that's correct, i don't know the answer but it's easy to see the ide of the current version is much more complex than flash 8 and that affects playback.