Using NEW on tables with generated columns I have a PostgreSQL 12 database, and in a table I created a column with a generated column, then I have a before update trigger that fires only if the NEW value is DISTINCT from OLD value, essentially this:
BEFORE UPDATE 
ON public.some_table
FOR EACH ROW
WHEN (NEW IS DISTINCT FROM OLD)
EXECUTE PROCEDURE public.update_modified_column();

However, this code despite being correct does not work with generated columns, giving the following error:

BEFORE trigger's WHEN condition cannot reference NEW generated columns

So my question is this: Is there any way to use NEW with a table that has generated columns without having to specify every single column of that table that isn't generated?
It can be something that requires specifying the columns that were generated to be excluded, just not the other way around.
Also, I know a potential alternative to generated tables is views (which are not the same thing but close enough for my use case), but I can't use views, since I need something that keeps track if the columns allows or doesn't allow for null values, which unfortunately views do not do that.
Using normal columns with a before insert/update trigger to calculate the columns, along with setting the columns as NOT NULL with a Default (for my use case ofc), has essentially fixed the issue; however, I will keep the question open to see if there is any solution to the generated columns specifically, since they are a bit more of an elegant solution.
That is simple: use an AFTER trigger instead. The column value will have been computed then.
On the other hand, your answers reveals that you need a BEFORE trigger because you want to modify NEW.
So probably the best solution is to use a BEFORE trigger with a WHEN condition that excludes the generated column:
WHEN ((NEW.col1, NEW.col2, ...)
      IS DISTINCT FROM
      (OLD.col1, OLD.col2, ...))