A bug occurs only when FEATURE_FLAG_NEW_UI=true . You don't want to commit that flag. You add it to .env.local , test the UI, fix the bug, then delete the line from .env.local . No traces left behind.

Note: System environment variables (variables set directly in your terminal or hosting provider panel) will always take precedence over files. Syntax and Structure of .env.local

Add your variables in a KEY=VALUE format. No spaces around the = sign.

Never, under any circumstances, commit .env.local . Why?