filter() expects you to use the raw PostgREST syntax for the filter values.
supabase.postgrest["countries"].select \{
filter(column = "name", operator = FilterOperator.IN, value = "('Algeria', 'Japan')")
\}
supabase.postgrest["countries"].select(
columns = Columns.raw("""
name,
cities!inner (
name
)
""")
) \{
filter(column = "cities.name", operator = FilterOperator.EQ, value = "Bali")
\}