Waveshare 3.5c screen not working after Raspberry Pi 4 firmware upgrade

[MrBroccoli]

My current zynthian daydream

Not off to a great start. Swapped in the SD card, the soundcard, and the screen from pi3… And instantly had a one of them “oh no, please no” moments. Blooming screen don’t work on pi4. I thought I had blown another one, but no… Swapped it all back to pi 3 and it was all fine… What could be wrong I wonder? As I’m trying to find out, a huge bee flies into my shed and bounces off all the lights. Luckily I had the pi 4 box handy and used it to help the bee back outside again.

See here