Base64 service only works as
a plugin for Penpot.
Try installing the plugin
by clicking here: Install plugin;
Or add it manually
to the Plugins manager:
Copy this URL:
https://tobase64.pages.dev/manifest.json
Open any Penpot file
(or create a new one)
Press Ctrl + Alt + P
(or use the toolbar
or main menu)
to open the Plugins manager
Paste the copied URL into
the input field in the modal
and click the "Install" button