Thank you for considering contributing to Flarum! Please read the Contributing guide to learn how you can help.
Active development is on the 2.x line — target 2.x for bug fixes, features and everything else.
1.8.x is in maintenance only mode until it reaches end of life on 31 December 2026. Until then only critical security fixes and critical bug fixes are considered for it; pull requests opened against 1.x for anything else will be closed, including ones that would previously have been accepted.
If you believe you have found something critical enough for 1.8.x, open an issue first so we can agree it qualifies before you write the code.