Hi Marc
Same happened to me on macOS.
I’m glad that I didn’t check the box to ‘delete previous version’ which I do with Illustrator and Photoshop. With Indesign I end up with multiple versions of the app because of the non-backward compatibility of major updates, not to mention it is the most crash-prone app I use – with the first indd file I opened and converted to v19 I’ve already had crashes caused by just moving an anchored object.
It’s quite annoying as none of the other Adobe apps with new versions this week had the same issue, but since Adobe had a warning box ready to pop up it’s clearly intentional/a bug they were aware of with this release.
While my file backup includes the whole preferences folder, I’m not going to chance introducing a problem if it looks like there’s a reason Adobe couldn’t import the v18 preferences file. I don’t think I have too many custom preferences and can at least open v18 and screen-shot each panel. I keep all my custom dictionaries in one place so manually re-linked those easily enough, and things like saved Find/Replace have shown up fine.
Nick