Appflowy has extremely poor performance. Both in terms of loading large files and RAM usage. See my performance comparison of block editors[1]:
I've built a block editor using Qt C++ and QML that is vastly more performant[2].
As you can see, Appflowy probably even has a memory leak, causing the memory to grow indefinitely in my test.
[1] https://imgur.com/ZL5QCS0
[2] https://www.get-plume.com/