You normally set Environment Variables in the Operating System, there are many entries in how it is done if you google.
(I thought I had posted this two days ago - apparently incomplete.)
Why do you think this is an environment variable? Did you see some message during debugging naming this thing? If so, it is internal to the Fortran Expression Evaluator (FEE) and is not something you can change. What is the situation where this occurs? Can you show a screenshot of the message?
The manuals says clearly the FFE is set to 500 and if this is insufficient change the environment variable.
From the web site I linked to
If a location in the source code has more than that number of locals, they are truncated and a note is shown:Note: Too many locals! For performance reasons the list got cut after 500 entries!The threshold can be controlled via the environment variable FEEMAXLOCALS.
It would appear that the programmers for the debugger have gone the traditional route of using an Environment Variable to hold a value that is not often used by the program. This is a good solution, the code is likely written in C++ and so it is easy to set the variable and it is easy to retrieve. They did not add it to the main window bars, which suggests it is not something they want people to play with at all.
There are very many web pages that show you how to set an environment variable for your version of Windows. I would set the FEE_MAX_LOCALS and FEEMAXLOCALS to your number, it has two names in two places. It is not going to bother Windows if you have both.
Humour is frowned upon in this august group.
As Caesar saying - Et tu Brute, or something similar from the Greek.
can be interpreted as a complaint containing a "suggestion of mimetic compulsion"
One could argue with some humour that the use of a single Environment Variable in VS and the debugger is copying something the programmer probably learnt in University or from an old master.
Of course there are several old masters here, they just paint in Fortran and do not make millions.
I rather think that it is actually what van Gogh said when he cut off his ear.