A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
I'm not very familiar with LogMeIn but it may be that remote access does not support the use of keyboard shortcuts, especially when dealing with different operating systems & differing keyboard mapping.
When working on a locally installed version of Mac Excel both Command+T an the F4 key should toggle absolute reference. However, if your Mac has a condensed keyboard [such as an Apple Wireless] you may have to use fn+F4 unless you make a change in System Preferences... Apple has defaulted the "F" [as in Function] keys to perform system operations (screen brightness, volume, etc.) rather than acting as regular function keys.