updates and versions - files not opening

I updated to InDesign version 18.2.1 twenty-one days ago when it came up. Then, two days ago a new update said it was available. I installed that, but it now says it was for version 17.4.1. I tried to open a file I myself created on the new document and it says it cannot open it because it was created on a newer version. The "convert" option does absolutely nothing (I've waited for more than enough time; it just greys out). I have checked every single way I can to for updates and it says that everything is up to date. So I'm stuck with being unable to open this file. I've restarted, closed and opened.... I'm stuck.