Perhaps USING syntax could be used for joining in the subqueries of derived tables

WITH views AS (SELECT 
views.table_schema, 
views.table_name, 
'VIEW' AS type,
views.view_definition
FROM 
information_schema.views
WHERE table_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
UNION SELECT schemaname, matviewname, 'MATERIALIZED VIEW' AS type, definition
FROM pg_catalog.pg_matviews),
views_processed AS (SELECT
table_schema,
table_name,
type,
view_definition,
regexp_replace(view_definition,'[\r\n]','<br>','g') AS view_definition_changed
FROM views)
SELECT table_schema, table_name, type, view_definition_changed AS view_definition
FROM views_processed
WHERE view_definition~*'JOIN'
AND view_definition!~*'USING[[:space:]]*[(]'
ORDER BY table_schema, table_name;