Is a big yellow, Heirloom Boston Pickling Cucumber past its prime already?

Question

We haven’t been keeping up with our square foot garden

Answer 1

Yes, this is past ripe.

Sometimes you can use a ripe cucumber for relishes; but if it is mushy I would just compost them.

https://www.gardeningknowhow.com/edible/vegetables/cucumber/when-to-pick-a-cucumber-how-to-prevent-yellow-cucumbers.htm