Hey there,

Thanks for sharing your screenshot! This looks odd, you should be able to see the constraint feature in the design panel. Would you be able to share a copy of your file so we can have a better look at it?

If you are hesitant to share publicly, you can reach out directly to the support with a copy of your file: here (please invite support-share@figma.com to the file with “can edit” permissions so we can take a further look. Please note this will not count towards your billing.)

As a reminder, here’s guide how to use constraint: https://help.figma.com/hc/en-us/articles/360039957734-Apply-constraints-to-define-how-layers-resize#apply

About the fill container, you’ll need to click on the child object (not the parent frame) to be able to select “Fill container”.

Hope this helps!