Hi char
This is Apple’s application Gatekeeper triggering, since our application is not yet digitally signed by Apple.
The way to workaround is usually to right-click on the application, which should give you a second prompt where you can say “Open”
Edit: I got reminded that this is of course not possible on Sequoia… instead after you’ve tried to open the application, you should go into Settings → Privacy & Security, scroll down to the bottom where you should see something like “Pencil2D was blocked to protect your mac”. Next to it you can click “Open Anyway” which prompts a dialog where you again click “Open Anyway”.
After doing that Pencil2D should start
Updating the docs - (a start to at least) Update "run" docs for MacOS Sonoma Security by nrichards · Pull Request #37 · pencil2d/pencil2d.github.io · GitHub
EDIT: instructions website updated with this answer to char’s question Download | Pencil2D Animation