Cant boot sd-card in raspberry pi 4

A few days ago I bought a raspberry pi 4. I was hoping to just use the SD Card of my Raspberry 3b+ and everything will work fine. (I also updated to the newest Buster version (sudo ncp-update and sudo ncp-dist-upgrade) - newest versions already installed. So I researched on the official website that the boot loader maybe is corrupted (of my new pi4)

https://www.raspberrypi.org/documentation/hardware/raspberrypi/booteeprom.md

But when I install a fresh raspbian on another sd card, everything works out of the box, so the pi 4 is properly booting.

When I plug the ncpi sd card in the pi 4, it wont boot (green led as indicator)

Anyone any idea what I could further try to get an image of my cloud sd card running on the raspberry pi 4?

kindly regards
crustulum

(edit)
I tried flashing the default image of nextcloudpi on another sd card an it worked. So there have to be something old, not longer supported option/“thing” that the pi4 cant boot the at the moment used system sd card. (it would be important, because I dont want to install the coturn sever again…)

I don’t have any practical solution, but @nachoparker might have some better insight. He is Nextcloud Sen-Pi :wink:

I have had it in the past where going from an older Pi to a newer Pi required I reinstall my OS. This was going from the Original Pi B to the Pi 2 B though so it’s been a while. The 3B+ is ARMv8 arch and the new 4 is ARMv8-A so it could even be that there is an architectural difference that would require the OS be compiled specifically for the different arch? I haven’t researched this, but that is one thing that comes to mind.

And this is my opinion and personal experience, but dist-upgrades are evil with Linux. So many unknown hidden gotchas. I’m a firm believer that Linux was never made to be upgraded from release to release, only replaced.

I haven’t tried this, but it makes sense that you need an updated kernel in your old SD card before it being able to boot. I would ask in the Raspberry Pi forums how to achieve this.