Migrate custom login logo and background from old server to new server

can anybody help me?

I had Nextcloud 16 installed on a QEMU VM (ubuntu 16.04), but I migrated user data and database to another Nextcloud 17 installed in an LXC container (Ubuntu 18.04).

It turns out that the old server had a custom logo and login background and I couldn’t find these images to migrate to the new server.