What is the ruling on earning profit from watching advertisements that may contain impermissible content, even with the possibility of filtering them, and what is the ruling on profits obtained through referrals (people who register through me), and is it necessary to filter their ads, or is advising them sufficient?

If the subscription is free, and the advertisements are permissible and contain no Shari'ah prohibitions, then there is no objection to earning profit by browsing them or by attracting subscribers in exchange for a known commission. The strong presumption that subscribers will adhere to the regulations is sufficient. The sin of anyone who commits a forbidden act falls upon them, not upon the one who invited them to subscribe, unless it is known that the person will not refrain from the forbidden, in which case it is not permissible to assist them. Ruling on a specific company depends on knowing its system and conditions.