So far i had success pasting into the FileZilla this path: /home/myusername/.ssh/id_rsa (despite the Filezilla file browsing window is looking up for a PPK/PEM files), while possibly a ssh-keygen has to be run in order for it to work: https://internetlifeforum.com/showthread.php?6656-How-to-allow-password-less-SSH-access-how-to-push-copy-key-over-SSH

On Windows, one may use putty gen / putty SSH key gen IIRC.