Most opinions for DaFS content consist of ‘manche’ and ‘solche’ and similar determiners are put into the der-word category (without any flexibility). “Manche schönen Bäume” while other sources split der-like determiners into those taking weak and strong endings for the following adjectives. Especially, “manch/einig/folgend/viel/wenig etc.” are recommended strong endings:
Manche/einige schöne Bäume
However, colloquially and in Duden online the case for manche is somewhat varied with no concrete rule, offering both strong and weak.
Is there a more standard rule that will be correct regarding these types of pronoun/adjective? Or if there are other words/situations in which there is a variation in Beugung?