Hi and welcome to devnet forum
Is the result of this apparent wrong reporting that you cannot install Qt5.12.2 ?
Regardless of what the reporting mismatch and you can go ahead with the installation, just so.
Not sure how it is on Mac. However, you might want to check if there are different target platforms selected which you do not plan to use. I am on windows and most people see the large amount of disk space required. However, in most cases only a much smaller amount is required. The maintenance tool simply preselects all possibility for a targeted version.