How to permanently prevent Outlook for Mac from switching to the new GUI?

My biggest panic about the eventual demise of Legacy Outlook is that I have tens of thousands of emails in file folders for tons of different projects -- not to mention personal emails -- that I've saved. Yes, of course, some of that could go and I do periodically purge my stored email. But my entire professional history is saved and there are lots of times when I need to go back into my email to find something, the name of a person, or reference a conversation or issue that is preserved in this way. In New Outlook, those saved folders are gone. They are not on my desktop and I have no way to access nearly 30 years of personal and professional history.

This would be like someone walking into my house and burning my journals, notebooks, files, photos, and letters. How on earth is this okay?

I am not even sure how I could preserve this data in a way that I could access it. So, I'm just worrying and waiting for the other shoe to drop.

Usually when I get a forced and unwanted update, I just ignore it for as long as possible. Eventually, I have to log out of my computer and then I log back on and hope for the best. I just cannot imagine another company (other than Apple) where this would be considered acceptable practice.

Any suggestions or solutions??

Thank you. I had seen somewhere a method to get into Mac terminal to delete the update that must have downloaded. I would not have downloaded that update if I knew it was going to completely mess up my outlook and my outlook organization.

I believe someone on this thread posted how to do it on windows, but if someone knows how to do it on Mac, and can post those directions, I would appreciate it. I did attempt to contact Microsoft support and have gotten absolutely no response. I’ve noted that Microsoft support has not responded to the serious issues raised in this thread among others with the new outlook.

So, this terminal command just gets rid of the banner saying try it now, but does not prevent it from periodically forcing you to switch?