My first office software was WordPerfect and Lotus 1-2-3 on DOS. Then Lotus Smartsuite, Microsoft Office, OpenOffice, now LibreOffice, with occasional bits of Google Docs. I never had to be retrained.
Here's the thing, for 90% of use cases, those are all effectively equivalent. You really shouldn't need any retraining whatsoever. A spreadsheet's a spreadsheet, and a word processor is a word processor. You type the text in the box and then hit print or whatever. Nothing new to learn.
Now admittedly, there are some power user features which are different, which is why I said they're only 90% equivalent. But most people don't use those anyway. Yet they will intensely oppose using a different but 90% equivalent thing because they haven't spent years being trained to use it - even though it's almost exactly the same thing they're using.
It's just a weird and bizarre mental hangup that seems to be natural to many humans.
If you're in tech, you will see the same thing with programming languages, frameworks, applications, etc. And it's on both sides, not just the users, but also the people hiring them too. "Oh, you've only worked with WordPress, you haven't been trained in Drupal?" "Oh, that's PHP, I only work in Python." "Well we're looking for a Ruby developer, not a C# developer." "That's React, I only know Vue.js"
It's mostly all general-purpose programming languages, libraries, and frameworks. Sure some details are different. There's a bit of a learning curve. But if you are actually capable with one, then picking up another nearly equivalent alternative should not be viewed as some impossibly complex thing that will take years of retraining.