SQL maximum memory limit exceeded
Are your links supposed to show anything? Currently none works. 

TT is right, that setting is just for the Buffer Pool and some memory clerks. See docs. There are other areas and even services part of SQL Server package that use memory. 


  max server memory controls the SQL Server memory allocation, including the buffer pool, compile memory, all caches, qe memory grants, lock manager memory, and clr memory (essentially any memory clerk found in sys.dm_os_memory_clerks). Memory for thread stacks, memory heaps, linked server providers other than SQL Server, and any memory allocated by a non SQL Server DLL are not controlled by max server memory.


Suggestion: You've most likely allocated too much memory to SQL. Dial it down - suggest going down to 40 GB to let also the OS breathe. If you have any signs of memory pressure then you might need to turn the knobs for more memory.

If you don't have any problems or memory pressure signs, then SQL Server it's doing its job.

Articles on the subject:


https://www.sqlskills.com/blogs/jonathan/how-much-memory-does-my-sql-server-actually-need/
https://www.brentozar.com/blitz/max-memory/
https://www.brentozar.com/archive/2011/09/sysadmins-guide-microsoft-sql-server-memory/
http://www.sqlpassion.at/archive/2015/02/23/the-3-configuration-options-that-you-always-have-to-change-in-sql-server/
https://sqlserverperformance.wordpress.com/2009/10/29/suggested-max-memory-settings-for-sql-server-20052008/
https://straightpathsql.com/archives/2017/02/sql-server-max-memory-best-practices/
https://voluntarydba.com/post/2013/03/19/Is-my-SQL-Servers-memory-over-committed.aspx


Later edit, after your reply:

You need first to establish what's the problem. Is it the report itself that there's no available memory? Do your applications/queries really suffer due to low memory? Is it just a training exercise?

You playing with database settings might just have caused the buffer pool to be flushed and now the reports look cool, but apps may suffer.

See what's in that server's memory by running:


https://www.sqlshack.com/insight-into-the-sql-server-buffer-cache/
https://www.sqlskills.com/blogs/glenn/sql-server-diagnostic-information-queries-for-october-2017/


And after you find out how your server's memory is populated, only then you'll find out where's it spent and if you have a problem.