Friend’s computer? His everyday PC? it must be a really good friend …
Acronis True Image 2020… Create a copy encrypted aes-256, then for paranoia purposes insert into the veracrypt encrypted(aes-twofish-serpent) container then send the file to a friend’s computer using encrypted FTP (ftps / TLS).
Check out restic. It encrypts repositories by default and you can set up remote and local repositories. Obviously you’ll need some transfer protocol with a server running on your friend’s PC, you could use ssh or the inbuilt REST server.
I have heard good things about Duplicati, although my internet speed is too slow for me to upload a backup in a reasonable time so I don’t use it myself.
LTT did the backup to a “friends” ( actually it was Jake, and employee ) NAS ( and identical Synology NAS ).
And they were using software provided ( downloaded from Synology ) by them.
Yes it allowed encryption on Linus’s side and Jake couldn’t even open the folder ( IIRC ) without the password ( don’t know what the encryption level is ). And they did it on Windows.
Don’t know if it will work if the receiving end is a non-Synology NAS. So it may not work with some other “random” NAS.