I’ve noticed that you don’t respond much to the answers to your queries.

Your question cannot be answered quickly and would require some engagement. To start you off I will just point out the allergy information from two easy to find chains that you could subsist on during a 4 day trip to Japan:

https://www.hanamaruudon.com/assets/pdf/allergy.pdf

and

https://www.ootoya.com/allergy/pdf/allergy1.pdf

Milk is the second column in the Ootoya list - 乳
Many (if not all) of the Ootoya branches have a tablet that can be used in English with lots of details about each item.
Here is a YouTube link where someone has posted how one can avoid allergens in an Ootoya order

+ And adding that MUJI’s own branded snacks have basic allergen information in English below the Japanese language ingredient list, this includes milk (I’m pretty sure meats are also highlighted). MUJI food items can be found at Lawson convenience stores and will be grouped together somewhere along with the other MUJI items.