To this end, for some it might be helpful to start with tracking spending (speaking from personal experience). I couldn’t determine what was a reasonable amount for a given category for a budget because I didn’t see my current circumstance.
I spent several years categorizing my expenses into two broad categories: fixed vs variable.
Fixed costs are utilities, mortgages, grocery, and insurance etc, variable costs were anything else (more or less).
By doing it this way I could see the minimum I needed to live—and also how much I was spending on frivolous shit.
Use Google Docs, and make a simple spreadsheet to track numbers. It doesn’t have to be a beautiful sheet, just functional. It will grow with you over time as you add and remove functionally to track different aspects of your finances that are important to you. If you don’t know how to use spreadsheets, online MOOCs have courses for a tiny amount of dollars relative to what you learn.