Summary

The Story Points field is of type free-form in Jira Software but, in Jira Align, it is a dropdown with pre-defined values (different than the Fibonacci sequence).
What happens with the sync if a value entered in Jira Software or Azure DevOps is not in the JA drop-down?

Solution

In Jira Align, the story points system is configurable at the level of the portfolio (under Administration> SETTINGs> Platform>Portfolio> Portfolio specific configuration> portfolio_name).

For Fibonacci, it uses the “Modified Fibonacci” sequence (1, 2, 3, 5, 8, 13, 20, 40, 100) which is the one used by Scrum/ScaledAgile.
The Modified Fibonacci sequence changes as the numbers grow to reflect an uncertainty with the estimation (with a focus on larger numbers). For further explanation see the following Estimating Stories on the ScaledAgile page).

The Jira and ADO Connector will handle the difference by adding any integer set in Jira outside of the modified Fibonacci sequence (such as 9, 10,11, 15, etc ..) to the Points fields.
Below is an example with the value of 11 now on the list.

Additionally, for any non-integer, the connector will round it off in Jira Align.
For example, a value of 1.5 will be rounded up to 2, 5.5 to 6 but 0.5 is rounded down to 0 while 0.6 to. 1.

Finally, Fibonacci or Power of 2 systems can be configured at the portfolio level.
Both behave the same way when new values, outside of the default Jira Align sequence, are inserted into Jira.