Learn English – The single word for “without any constraints”

One obvious word is simply unaccountable:

[Merriam-Webster]

2 : not to be called to account : not responsible

The only other single word I can think of—although it has a broader meaning than you might like—is

Exempt:

[Merriam-Webster]

2 : free or released from some liability or requirement to which others are subject • was exempt from jury duty • the estate was exempt from taxes

Of course, there are also some very specific contextual phrases. For instance, diplomatic immunity.