The wifi failure is arch-specific. On rasbian wifi is functionally out of the box.
With new kernel 4.19.58-1 and firmware raspberrypi-firmware 20190715-1 wifi doesn't work even with my workaround. No wifi adapter is found anyway.
To reaload the driver takes no effect. Here is my dmesg dump:
after $this->bbcode_second_pass_code('', 'modprobe -r brcmfmac'):
usbcore: deregistering interface driver brcmfmac
after $this->bbcode_second_pass_code('', 'modprobe brcmfmac'):
cfg80211: Loading compiled-in X.509 certificates for regulatory database
cfg80211: Loaded X.509 cert 'sforshee: 00b28ddf47aef9cea7'
platform regulatory.0: Direct firmware load for regulatory.db failed with error -2
cfg80211: failed to load regulatory.db
brcmfmac: brcmf_fw_alloc_request: using brcm/brcmfmac43455-sdio for chip BCM4345/6
usbcore: registered new interface driver brcmfmac
brcmfmac: brcmf_sdio_htclk: HT Avail timeout (1000000): clkctl 0x50
Downgrading only the kernel took no effect. There is something missing in or wrong with the firmware database ...