The list of devices that will receive updated BlueTooth support in RokuOS 11.5 (for outgoing audio connections) is larger than that posted by @makaiguy
Specifically, it also includes the Ultra (4800) and Ultra LT (4801) in addition to the Roku Smart Soundbar (9101) and ONN Roku Smart Soundbar (9100).
From the RokuOS 11.5 Release Notes: https://support.roku.com/article/228844467
Bluetooth Private Listening on Select Devices - Roku Ultra, Roku® Streambar®, Roku® Streambar® Pro, Roku Smart Soundbar, and onn.™• Roku Smart Soundbar owners will be able to connect their favorite wireless Bluetooth headphones directly to their device for easy access to private listening. Once paired, wireless headphones can be easily connected or disconnected in the Options menu, or set to connect automatically.
Note: Bluetooth private listening will be available on Roku Ultra (4800X, 4801X, 4802X), Roku® Streambar®(9102R), Roku® Streambar® Pro (9101R2), Roku Smart Soundbar (9101R), and onn.™• Roku Smart Soundbar (9100X) devices.