Please go to this Microsoft website and click Download tool now button, download Media Creation tool.
https://www.microsoft.com/en-us/software-download/windows10
This tool can assist you update system to the latest version 20H2, since you have update issue for many months, general check for updates will cost many time, use this tool can be faster. Why I don’t suggest to upgrade to 21H1, because this version of Windows 10 still belongs to Insider Previews version, it is aimed at Insiders for test and check potential issue, it is not a version for daily work and life.
On the other hand, you mentioned that there is a sentence: “Some settings are managed by your organization” appears in Settings but this is a personal device. This situation can be fixed by reset this PC. Once you upgrade to 20H2 version, check if you will still see this message, if it exists, reset this PC from Recovery.
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