Seems like you are in luck, replacing the wireless card is actually relatively easy and cheap. Here's a guide for replacing the HDD/SSD with an overhead camera, you can see the wireless card is there with the white/black wires connected:

www.youtube.com/watch?v=qP-YLXxgDO8

Your laptop requires a half height mini PCIe card. This is probably the best you can get with that form factor:

Intel ARK: ark.intel.com/products/75439/Intel-Dual-Band-Wireless-AC-7260
Amazon Link ($30): www.amazon.com/Dual-Band-Wirless-Bluetooth-PCI/dp/B01E85QIFI

I run linux on pretty much all my hardware, and I've been through a few laptops. You get used to replacing Broadcom/Atheros chips with better supported Intel chips whenever possible.
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The problem is persistent in all releases of liquorix 5.0.0.

However it does not occur in stock 5.0.0 kernels (both lowlatency and generic) shipped with Ubuntu 19.04 (disco).

So it seems that some change between liquorix 4.18 -> 4.19 caused this.
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I suspect your wireless card will continue to not work with Liquorix (and more specifically, MuQSS), due to the code quality of Broadcom's out of tree drivers.

Basically, MuQSS is more likely to prompt bad drivers to behave badly if they don't have controls in place to prevent racy conditions. The best drivers in the kernel are mainline (due to the strict quality controls of the maintainers), and used by a large majority of hardware configurations. Since your hardware is unique and relatively unpopular due to age, it's unlikely to get much more attention.

My recommendation still stands to replace the wireless chip with something more modern and common, the Intel 7260.
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