Hello and Welcome to our Open Community!
To manually purge cache on specific pages you will have to install Classic Editor plugin.
This feature is not yet compatible with the default Block Editor (Gutenberg).
This could also be the cause for the failure of the post/page cache clearing during content updates.
Have you tried this feature with the Classic Editor?
We will make it compatible with the Block Editor in the future, but this may take a while because development of this less popular and free plugin is low on our priority list.
Dessky Cache is the Free and Open Source plugin and you can help the development by becoming a contributor. If coding is not your thing then spreading a good word for this plugin also helps.