I converted Japanese to English with translation software.
I was able to load PNG sequences in my environment without any problems. I can advise you if you explain in detail.
1) Is it possible to export a PNG sequence from Adobe Character Animator? 2) Is it a serial number?
Step1 Start Animate2021. Step2 Create a "new" project. (Example: 1920 x 1080 24 fps) Step3 Select "Load"-→ "Load to Stage" from the menu. Step4 Select the file "Name.00.png" from the folder containing PNG. Step5 "This file is part of the sequence. Select ~" → "Yes". Step6 The sequence PNG is loaded into the timeline.
Although it is in Japanese, the commentary video has been uploaded to YouTube.