Mariadb function does not work in version 11.8

I don't normally see the syntax LANGUAGE SQL in stored procedure or function definitions on MySQL or MariaDB. Try removing it:

CREATE FUNCTION fnGetLevel (
    pNodeKey VARCHAR(1000)
)
RETURNS INT
DETERMINISTIC
NO SQL
BEGIN
    RETURN LENGTH(pNodeKey) - LENGTH(REPLACE(pNodeKey, '/', '')) - 1;
END;

Hypothesis: Incorrect parsing of multi statement DDL. You can try to use function without BEGIN END block so there is only single ;:

CREATE FUNCTION fnGetLevel(pNodeKey VARCHAR(1000))
RETURNS INT
LANGUAGE SQL
RETURN LENGTH(pNodeKey) - LENGTH(REPLACE(pNodeKey, '/', '')) - 1;

dbfiddle demo

If the same function works on MariaDB 10.6 but fails on the 11.8 server at RETURNS, I'd first verify that the UAT server is actually running MariaDB (SELECT VERSION();) and not MySQL or another compatible database. Also check that Liquibase is sending the function as a single statement. As a quick test, try removing LANGUAGE SQL and use DETERMINISTIC NO SQL instead. If it still fails, the issue is likely with the server/environment rather than a MariaDB 11 syntax change. Posting the exact SELECT VERSION(); output and full error message would help pinpoint the cause.