Is possible to replace the system font (Roboto) to San Fransisco font without rooting my Nokia 6.1+?
Roboto-Regular.ttf to SF-Regular.ttf
Roboto-Bold.ttf to SF-Bold.ttf
Roboto-Heavy.ttf to SF-Heavy.ttf
and so on...
I have done it successfully on rooted devices
You will naturally need root to replace a system font. Because without root, you cannot write to the partitions where the fonts are stored and loaded from.
So, in order to answer your question - No, it is not possible.
That said, we do hear that Android Q will have support for font changes. If the feature makes its way to the final Q builds, you will be able to do font modifications when it hits your device in the coming months.