Teaching the concept of spreadsheets is totally possible without teaching students products of whatever specific corporation donates the most money or free licenses.
Libre also has different features than Excel which has different features than Sheets, etc, but Excel is the "standard". You're going to see Excel far more than Sheets in the workplace and I've never seen a job listing mention Libre Calc.
I know Excel, I started at a startup 4 months ago using Sheets, the first few weeks I had to 'unlearn' half of what I knew and try and figure out how to do similar in Sheets. If I only knew sheets, I'd probably have been even more lost going to Excel because Microsoft doesn't hold your hand like Sheets does with every formula you start to type. I'm guessing something like Libre Calc is worse than Excel and Sheets in that regard.
>Teaching the concept of spreadsheets is totally possible
Sure, but teaching someone to drive a 4-cylinder automatic driver's ed car doesn't prepare them to say operate a manual tri-axle or a an excavator. Sure they understand steering, acceleration and stopping, but all of the unique mechanics of say Excel are different than random free software.
Nothing at the level students do spreadsheets is different between spreadsheet programs
The hard thing is to find the book (with the information you want) and not reading the book itself (that was before google/inet)
Pretty sure this is how we wound up where we are.