So if it is May and your birthday is in July.If I said “I’ll see you Monday” that would assume the 23rd. The ‘next’ is completely redundant.
“I’ll see you next Monday” would make more sense as it implies the Monday after the coming Monday.
Monday - This Monday, the 23rd.
Monday - The next Monday in the series of Mondays. The 30th
Monday
Monday
Would your upcoming birthday be your next birthday or is your next birthday the following year?