That’s not correct for the server:
contains
Distribution stretch-5.0
with the note
The Tryton client 5.0 is not compatible with the library versions available in stretch (nor in stretch-backports) and is thus currently not usable on Debian stretch.
So you can currently deploy the server 5.0 on stretch, but for the client you have to use buster, because the client is not compatible with older versions of libgdk-pixbuf2.0-0 (see also Tried to install tryton, but it segfaults). As a workaround you could still use a VM running buster on a stretch host.
Tryton Debian Apt Repository — Tryton for Debian 6.0.0 documentation links to
It’s for sure not drag&drop, but may be of some help to you.