Catalina cannot be installed in Macintosh HD

You’re welcome.

Hopefully you now realize that based on the information you provided in your first and second posts, there is no way anyone would have realized APFS might possibly be an issue, as that conversion occurred with MacOS High Sierra in 2017.

MacOS Sierra is now quite old. It was released in 2016. Since then, much has changed including the format of the Macintosh HD disk.

See especially “About APFS and Mac OS Extended” here.

How to erase a disk for Mac - Apple Support

In the future, you should update your Apple software much more frequently to keep up with the latest defect repairs, security enhancements, feature additions, and avoid an enormous jump in operating system such as you’re attempting here.

Well, there are still huge amounts of information you know and we don’t.

I’ll provide just a few examples, but then I expect to give up on this thread.

• What year is this Mac?
• Has it ever had a previous operating system? Which version number?
• What disks and/or solid state drives are involved?
• What was on them previously?
• Did you get the Catalina download in the App Store?
• Has there been some change of Apple ID involved?

We need many more details.

Writing an effective Apple Support Commun… - Apple Community