Raging_Moose
Greenhorn
this might help, might not it worked for me. open up your windows defender, then go to Firewall & Network Protection, then select allow an app through firewall, in the next window scroll down the list till you find Stardew Valley and select it, then click the remove button, then ok. after you have done all that start Stardew Valley up and open your coop world you are hosting, this will trigger you needing to reestablish your connection permissions for Stardews Valley. this might fix your issue and allow others to connect