Did you unlock your bootloader? Some apps just scan for Google Play SafetyNet or in some other way to check whether you unlocked your bootloader or rooted and if they think you do they will vaguely state you are rooted.
Other's concern about your phone being infected are justified and I recommend you to try whether a dedicated root checking app thinks your phone is rooted. These usually don't lie.
Regarding your rooting situation I always rooted the lazy way. Renamed magisk.apk
to magisk.zip
, flashed it and it always worked for me. But I rooted only 2 phones in my life really and this is not the recommended method by magisk developer.
https://topjohnwu.github.io/Magisk/install.html