The premise is ridiculous imo. Yes, banks are exploitative, but the reality is that we must do what we need to so we can survive. The saying "there is no ethical consumption under capitalism" extends to every facet of life. An emergency fund placed in a bank account is a good idea to ensure you can maintain a minimum standard of living.

As for investing, here in the US it's damn near impossible to retire without a 401k investment portfolio. I would like to not work some day, so I need to invest. One of the most insidious parts of capitalism is how it compells unwilling people to participate through the state apparatus. Remember, Engels was a capitalist and bankrolled Marx to get the revolution running. Having money isn't a bad thing, until it's time to abandon the need for money.

We set our money on fire each day, as the good lord intended.

Practically speaking, not investing your wealth means giving money to the state (who currently will just give it to the richest and most powerful) and the richest and most powerful.

The entire monetary system is set up to take from the bottom 80-90% through inflation and give that money to anyone who invests and profits off of debt.

I know it sounds stupid, but that's the way it is.

The only other option is immediately putting your savings into gold, practical investments (like a solar setup) or commodities.

As long as you hold any significant amounts of savings, it slowly (and recently more rapily) goes to the state and the rich. Nevermind your wages are constantly decreasing too. You could make up for that by investing. You could see it as just getting back what's rightfully yours anyway.

Reality is silly like that in an inflationary monetary system.

So, what is an ethical stock or fund to buy?

Buy land and deed it to one of the trees on it.

Generally you should do what:

1. Maximizes your personal well-being (though note I'm not saying "wealth", because they two are not always the same), and
2. Satisfies your personal and ideological principles as well as possible, at least to the point where you can live with yourself.

Just because we have systemic critiques doesn't mean we should go live in a cave and eat bugs. To the degree possible we should prefigure the society we want to build, but torturing ourselves individually to do it is both unproductive and likely takes away from our focus on more important things like organizing and taking direct action that impacts the system. We do tend to make personal sacrifices to further our ideological goals, but there's both a practical limit and one where we shouldn't be cruel to each other in our expectations.

Many of us are vegans. Most of us probably avoid buying shares in oil companies. But all of our circumstances are different. Perhaps people salting Chevron to radicalize union organizing there will wind up with its stocks in their retirement accounts that are difficult to divest from without harming their ability to retire, due to their particular circumstances. It seems pretty shitty to expect someone to just get rid of them without us having some kind of dependable (e.g. mutual aid) infrastructure in place to take care of each other in our old age.

TL;Dr: Yet you participate in society. Curious!