That gives me:
$ sudo apt-mark unhold yunohost
yunohost was already not hold.
$ sudo apt-mark unhold yunohost-admin
yunohost-admin was already not hold.
$sudo apt install yunohost yunohost-admin
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
yunohost : Depends: python-requests but it is not going to be installed
Depends: openssl but it is not going to be installed
Depends: ca-certificates but it is not going to be installed
Depends: libnss-ldapd but it is not going to be installed
Depends: libpam-ldapd but it is not going to be installed
Depends: postfix but it is not going to be installed
Depends: postfix-ldap but it is not going to be installed
Depends: postfix-policyd-spf-perl but it is not going to be installed
Depends: postfix-pcre but it is not going to be installed
Depends: dovecot-core but it is not going to be installed
Depends: dovecot-ldap but it is not going to be installed
Depends: dovecot-lmtpd but it is not going to be installed
Depends: dovecot-managesieved but it is not going to be installed
Depends: dovecot-antispam but it is not going to be installed
Depends: rspamd but it is not going to be installed
Depends: metronome (>= 3.14.0)
Recommends: python-pip but it is not going to be installed
E: Unable to correct problems, you have held broken packages.