what Windows upgrades are possible despite that are unsupported by Microsoft?

[Sergiaws]

I want to know what upgrades/downgrades are achievable without doing a clean installation despite that Microsoft don't provide/support it. Here are the possibilities.

1. Windows 9x/2000 to Vista/7+

2. Windows XP to 7/8/10/11

3. Windows Vista to 8/10/11

4. Windows 7/8/8.1 to 10 (LTS versions) and 11

5. Interesting upgrades through Windows Alpha/beta builds.

And, what about these downgrades? Are possible without doing a clean installation?

1. Windows 10/11 to Windows 8.1 and older

2. Windows 8.1 to Windows 7 and older

3. Windows 7/Vista to XP and older (theoretically it is possible to downgrade Windows 7 to Vista).

4. Windows XP to 2000, maybe downgrade to Windows 9x will be very difficult.

5. Curious downgrades through alpha/beta builds.