I was running into the same issue with my Raspberry Pi Zero 2 W. After updating from DietPi 9.12 (?) to 9.15 on August 4th load had increased from 0.2 to 1.2. Because a lot of compute time was spent on the processkworker/u21:0-brcmf_wq/mmc1:0001:1 I thought it was related to the wifi driver.
I got a hint that the high load might be related to this topic. And it was. After applying the workaround provided by @MichaIng on August 5th load has fallen to somewhere between 0.2 and 1. Interestingly that is not as low as before the update but lower than without the patch. But thanks for that!
Now I wonder whether the workaround will be provided as patch in one of the next updates or whether the workaround is the final solution.
