1) Is it permissible to buy shares of non-Muslim banks?
2) Is it permissible to buy shares of social media companies when they generate revenue from advertising that may include alcohol products, gambling etc.?
In both cases, if you can stipulate a condition in the agreement with the company that you will only partake in shares that do not involve religiously unlawful transactions, such as dealing with alcohol and usury, then it is permissible to buy the shares, otherwise, it is not permissible.