I have completed all the required modules of trailmix 3 and 4. Nothing is left to solve And still, it shows incomplete😟. What should I do?

Please try the below steps.

Please open all the challenges one by one and check if any module is pending.

Clear the cache.

Try in incognito mode. 

If nothing will work then you can raise the case. 

https://trailhead.salesforce.com/help?support=mycases