It's tricky because some projects are hobby, spare time where earnings come from "a real job" and for devs to earn enough to reasonably live on would need serious donations from users depending on quantity of users. There are real niche markets and apps that can only exist due to benevolence.
As a rule of thumb, Businesses that use computers in their operations should be planning to spend between $50 to $100 per month per seat on average to support their needs, spread across all their backoffice needs (os, office suite tools, diagramming, coding IDEs, graphics tools, email, file share, backups etc). Obviously businesses with dedicated focal points will tend to spend more in given areas. So based on that, can plan for your own needs and donate to projects you find instrumental in your day to day life.
My recommendation here is to assess periodically (annually, maybe as often as quarterly), and send some dollars, sats, whatever. For me it's projects like Gimp, LibreOffice, VLC. Most projects don't take sats, but accept payment via credit card
