adding a generated column to a table?

If I have a table containing a date field, say:

create temporary table tmp1 as select now()::date as evtdate;
SELECT 1

select DATE_PART('year', evtdate)::integer as year from tmp1;
 year
------
 2024
(1 row)

Is there some way of doing something like the following?:

alter table tmp1 add column year integer generated always as DATE_PART('year', evtdate)::integer STORED;
ERROR:  syntax error at or near "DATE_PART"
LINE 1: ... tmp1 add column year integer generated always as DATE_PART(...