What is the current state (2022) of using UDFs in a CHECK constraint in SQL Server?

SQL Server allows the use of User-Defined Functions (UDFs) in CHECK constraints - which has a number of use-cases - which I won't get into - but I was recently faced with implementing a non-trivial business/domain constraint that validated data in one table based on non-unique, non-key data from another table - which means the constraint cannot be implemented using any of the built-in constraints (FOREIGN KEY, UNIQUE, or a normal row-value based CHECK constraint).

My immediate go-to was a TRIGGER, as Microsoft's own documentation states that TRIGGER objects are the intended way to implement non-trivial constraints:

DML triggers are most useful when the features supported by constraints cannot meet the functional needs of the application. [...] Unlike CHECK constraints, DML triggers can reference columns in other tables. For example, a trigger can use a SELECT from another table to compare to the inserted or updated data and to perform additional actions, such as modify the data or display a user-defined error message.

Hang a second: Microsoft wrote "Unlike CHECK constraints, DML triggers can reference columns in other tables" - but that's misleading! CHECK constraints can reference columns in other tables indirectly via a UDF.

...so methinks there's a bit of vague and outdated information out there - so let's do more research to see if CHECK constraints with a UDF is the right way to go or not...

...well, it seems that UDFs in CHECK constraints seem have a bad rep: with critical remarks concerning poor performance and their lack of formal correctness (a winning combination...), but I noticed that the articles and posts I read, including practically all of the Google search results concerning UDFs and CHECK constraints was just old...

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The #1 Google search result for "sql server check constraint udf" is an article dating back to 2001 - which doesn't give any performance advice, but the fact this is still the top result shows there's

Partial answer. Requirements to inline scalar function specifically states it cannot be in a computed column or check constraint.

The UDF is not used in a computed column or a check constraint definition

StackExchange Database Administrators Q#313310, answer score: 2