You can technically charge for FOSS, but that sort-of collides with the freedom to redistribute the software. You may have heard about that when the whole RHEL/Rocky Linux dispute happened.
Equal shares can also be kind-of unfair if your backend is using sqlx for the entire database communication and then you also use some small image-conversion library to convert the favicon from .png to .ico.
My last point may be a bit confusing, let’s try to make it a bit easier to understand: In this case, you are a company, that is directly using a piece of code that is licensed under the license you’ve been thinking about, and you’re also using a piece of proprietary software, e.g. some ERP-Software. The proprietary software is using a FOSS library that permits it to be used in a proprietary binary, let’s say because it’s BSD-Licensed. How do you know that the ERP-Software is using that library, and how would you determine how much you’d have to donate to them. You kind-of have to donate to them, because your ERP-Software wouldn’t run without that library