[Solution] After flashing the modified boot of Magisk, magisk still has no ROOT.

1. Check whether the /system/bin/su file exists. If it exists, execute the following:

 setenforce 0

2. If the /system/bin/su file does not exist, then execute
 

cd /system/bin

ln -s  ./magisk su

setenforce 0

3. If 1 and 2 above don’t work, try this method.

Name the following code su, and then push it to the /system/bin directory of the android device

#!/system/bin/sh
#echo "count =$#"
#chcon u:r:magisk:s0 /system/bin/su
#chmod 777 /system/bin/su
#chown 0.0 /system/bin/su
if [ $# == 0 ]; then
	magisk su
else
	magisk su -s $@
fi

Then, chmod 755 /system/bin/su can root and run normally.