PL/pgSQL doesn't support variables in queries?

ms-sql person here migrating over to pgsql. One of the first thing's I noticed with pgsql (or more specifically, PL/pgSQL) is that it doesn't support "variables" in a query?

for example, here's some T-SQL:

DECLARE @fkId INTEGER

SELECT @fkId = fkId FROM SomeTable WHERE id = 1

-- and then do something with that value..

SELECT * FROM AnotherTable WHERE Id = @fkId

SELECT * FROM YetAnotherTable WHERE FKId = @fkId

-- etc..

If I have this information correct, has this concept ever been discussed before or considered to be included in PL/pgSQL ?

Thank you kindly for any help/conversations on this topic.

Sincere apologies if this is not the correct forum/list to ask this question.

Regards,

JA.