Raspberry Pi 3B 1.2: bluetooth issues

[bjo]

Hi,
I recently got a Pi 3B 1.2 and put the MicroSD used in a Pi 2B into it. It boots fine, but bluetooth isn't visible. So I tried the aarch64 image with the mainline kernel, bluetooth is usable, but after some short time connection issues appear streaming A2DP, dmesg is full of hci0 tx timeouts.. The net is full of issues, it seems the problem is caused by the coexistence of bluetooth and wifi and should be fixed by putting

$this->bbcode_second_pass_code('', '
btc_mode=1
btc_params1=0x7530
btc_params8=0x4e20
')

into brcmfmac43430-sdio.txt. But in my case, it does not help and wifi isn't used at all.

So, what is the best way to use the builtin bluetooth of a Pi 3B? Is it still needed to use the pi-bluetooth-PKGBUILD as stated in the wiki? According to some comments, the package is obsolete and it shoudl also work out of the box with the armv7h-image?

Edit: Trying now the linux-raspberrypi4-kernel with
$this->bbcode_second_pass_code('', 'dtparam=krnbt=on')