Yes. Can I install it on a client's server to show a demo? Yes, provided the demo is not the production environment. Can I use it for my production database if I don't make money? No. If the database serves users (even if the app is free), you need Express (free, limits apply) or a paid license (Standard/Enterprise). Developer is strictly for building and testing.
-- Check server edition and version SELECT SERVERPROPERTY('Edition') AS Edition, SERVERPROPERTY('ProductVersion') AS Version, SERVERPROPERTY('ProductLevel') AS ServicePack; sql server 2019 developer edition