Hi all,
I know co-design was quite big about 10 years ago in the UK. The Kings Fund did some work on this, which has now been ported over to the Point of Care Foundation. A toolkit is available here:
https://www.pointofcarefoundation.org.uk/resource/experience-based-co-design-ebcd-toolkit/
Keep in mind there are other terms that might be used, depending on the field of the originating theory - participatory design, co-creation etc.