Comment 3 for bug 1875475

Note that I solved the incompatibility issue with Windows & Mac OS by installing the former Debian version on the Ubuntu 20.04 LTS server:
```
wget http://ftp.fr.debian.org/debian/pool/main/u/unison/unison_2.48.4-1+b1_amd64.deb
sudo dpkg -i unison_2.48.4-1+b1_amd64.deb
```

Running that breaked the compatibility with Unison from the Ubuntu 20.04 LTS client. To solve that, I ran the previous command on the Ubuntu client as well, plus this one:
```
wget http://ftp.fr.debian.org/debian/pool/main/u/unison/unison-gtk_2.48.4-1+b1_amd64.deb
sudo dpkg -i unison-gtk_2.48.4-1+b1_amd64.deb
```