Just working with Photos and found the Filter option. Looking at Library Albums or Shared Albums you can find the ( ... ) button in the top right corner and see several menu items. The menus change depending on the current view. For example:
- Library > Months > ( ... ) >
- Albums > view an album > ( ... ) > Filters >
- Albums > Shared Albums > view an album > ( ... ) > Filters >
[We can expect new menu items to appear with future iOS updates.]
The little icon for Filter is available in other apps.
Frame Grabber is the app recommended to save a still frame from a video clip. And from Live Photos! Also from Timelapse or SloMo videos. Individual frames are saved as HEIF to Photos or to Files app.