GNU/Linux Installing Broadcom BCM4350c5 Firmware Guide
How to Install Broadcom BCM4350c5 Wireless Bluetooth Driver Firmware on GNU/Linux Systems – Step by step Tutorial.
And the BCM4350c5 Devices are supported by the btbcm Kernel Module on Linux 4.15+.
But what may be easily missing is the needed Proprietary Firmware.
In any case to get the possible Newest Patches, Fixes, and Improvements you are strongly Recommended to Update System & Kernel.
On Arch Linux based see instead: AUR Package Installation.

1. Updating System
How to Update System on GNU+Linux
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