What needs to be done to run a macro created in 1999 in Office 365 Excel correctly?

[BillN33]

Created an extensive macro (Excel 1997) in 1999 consisting of several modules run together using "cntrl, shift, letters". Have been able to run it successfully ever since until recently, and it now gets bogged down and runs ever so slowly. The original spreadsheet that I've continued to use has a .xls file extension. 

I recently saved the spreadsheet with the .xlsm file extension but it makes no difference and will not recognize the quick access keys. Seems to have begun with the latest Windows 'update'. Will I have to rewrite the macro in VB or is there a simple fix?

[#2]

@BillN33  I'm glad I'm not the only one noticing Broken VBA Macros in Excel! I used one from Microsoft's site to record Calculation Time for a CPU Benchmark. Their Macro breaks now and doesn't even load properly now. I was working until two or three  weeks ago. Here is their macro I was using - Microsoft's VBA Macros Don't Work in Excel Anymore!

SITE:MICROSOFT.COM - Excel performance: Improving calculation performance

Here is my Real World CPU Benchmark which no longer works with their VBA Macro.

https://intensewebs.com/index.php/benchmark/real-world-cpu-performance-checker-excel

[#3]

@BillN33P.S. In addition, and at the same time as breaking the VBA Macros, the Formula Calculation times decreased by 30%-40% on AMD Platform and by 10%-20% on Intel Platform. This all happened in last 2-3 weeks.