Strawberry jam (hopefully)

I think it's recommended to use over-ripe strawberries for jam Can't remember the reason.
We once made some with fresh strawberries and it wouldn't set. So reheated and put in a Rowntrees jelly cube. It set, but wasn't authentic.

I have used lemon juice for a set.
They should be fine because they go soft when you cook them anyway - or in smoothies?
Don't throw them away

I have done it, but needed pectin for the set.