Hey. this solution worked for me thank you!. i want to note that i couldnt find the magisk app on the appstore so you have to google it and got it myself from magiskmanager.com and installed the apk.
For other people you can find the fairphone 4 rom on the official website which contains the boot.img also when patched it will look a little like this “magisk_patched-26100_qXhxI.img”
If someone is technical enough to do this but is strugging to get it working ill offer my assistance for a short while.