@raf no, that’s not it. You need an Rpi4-specific image. Do like this:
Find out where MagicMirror is installed. I’ll use
~/MagicMirror in the below. (~ is a shortcut to your home directory)
Go to your home directory by entering the command:
cd
Make a full backup of you MagicMirror installation by entering the command:
tar czvf mmbackup.tgz MagicMirror
This will create a file call
mmbackup.tgz
Copy the file
mmbackup.tgz to another computer or usb stick. There are several ways to do that, google if you don’t know. The important thing is that you do
NOT store it on the SD card. The easiest way is probably to use an USB stick. Insert the stick into the Rpi3 and Raspbian will normally automount it. I will assume that the stick is mounted as
/mnt/usb. If so then copy the backup with the command:
cp -vi ~/mmbackup.tgz /mnt/usb
On you Windows computer, download a raspbian image for Rpi4.
Insert your SD card and write the image to card using
Etcher or similar program (The same as you did when creating the SD card for the Rpi3)
Move the SD card to the Rpi4 and complete the install.
Copy the file
mmbackup.tgz from wherever you put it to your home directory (~). If you used an USB stick in step 4 above then you can use the command:
cp -vi /mnt/usb/mmbackup.tgz ~/
Unpack the backup with the commands:
cd
tar xvzf mmbackup.tgz
Follow the instructions at
https://docs.magicmirror.builders/getting-started/installation.html to complete the install. Skip step 2 as you have already installed MagicMirror.