According to the US Department of State in 2021, "The law does not provide for freedom of association. The law requires formal groups, including religious, social, business, labor, and cultural organizations, to register with the Registrar of Societies and provide regular reports on membership and finances."

References:

2021 Country Reports on Human Rights Practices: Brunei: https://www.state.gov/reports/2021-country-reports-on-human-rights-practices/brunei/