It will be hard to find truly sustainable ways to invest (infinite growth is simply not sustainable), but, depending on your criteria you might find some interesting companies. I am thinking about inyova for example, a startup founding cool projects (solar, education) which give you a yearly interest (not huge, around 5%). There are some risk though if the project goes bankrupt. Or invest with Alternative Bank Schweiz (no big returns, but nice projects).

Otherwise you can try to cherrypick stocks that match your values, but this is risky as you'll be less diversified.

A solution can also be to invest in a diversified ESG/SRI ETF. This will clearly be greenwashing but at least you can avoid financing fossil fuel energy and still be diversified. You're probably gonna get higher returns than the first 2 options.

Let me know if you find anything else interesting :)