Install OpenSSH into home directory from source

openssh.md

wget https://cdn.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-8.0p1.tar.gz
tar -xvzf openssh-8.0p1.tar.gz
cd openssh-8.0p1
./configure --prefix=$HOME --with-privsep-path=$HOME/var/empty
make
make install

The --with-privsep-path=$HOME/var/empty is necessary to avoid an error like:

openssh "cannot create directory ‘/var/empty’: Permission denied"

cf. https://openssh-bugs.mindrot.narkive.com/kl4ICqSS/bug-2940-new-installing-in-home-should-not-require-root-privileges#post2