Impossible de re-installer libreoffice

Je travaille sur Mint 19.3. J’ai voulu installer une version récente et j’ai choisi la version 7.6 qui crachait à chaque fois quand j’appuyais sur le boutton “Aide”. En voulant passer sur la version 7.5 la désinstallation a mal fonctionné et
apt-get purge libreoffice
donne
Package ‘libreoffice’ is not installed, so not removed
0 to upgrade, 0 to newly install, 0 to remove and 5 not to upgrade.
sudo apt-get install libreoffice
donne
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.
libreoffice : Depends: libreoffice-base but it is not going to be installed
Depends: libreoffice-calc but it is not going to be installed
Depends: libreoffice-core (= 1:6.0.7-0ubuntu0.18.04.13) but 4:7.6.2~rc1-0ubuntu0.18.04.1~lo1 is to be installed
Depends: libreoffice-draw but it is not going to be installed
Depends: libreoffice-impress but it is not going to be installed
Depends: libreoffice-math but it is not going to be installed
Depends: libreoffice-report-builder-bin but it is not going to be installed
Depends: libreoffice-writer but it is not going to be installed
Depends: libreoffice-avmedia-backend-gstreamer but it is not going to be installed
Recommends: fonts-crosextra-caladea but it is not going to be installed
Recommends: fonts-crosextra-carlito but it is not going to be installed
Recommends: fonts-linuxlibertine but it is not going to be installed
Recommends: fonts-sil-gentium-basic but it is not going to be installed
Recommends: libreoffice-librelogo but it is not going to be installed
Recommends: libreoffice-nlpsolver but it is not going to be installed
Recommends: libreoffice-ogltrans
Recommends: libreoffice-report-builder but it is not going to be installed
Recommends: libreoffice-script-provider-bsh but it is not going to be installed
Recommends: libreoffice-script-provider-js but it is not going to be installed
Recommends: libreoffice-script-provider-python but it is not going to be installed
Recommends: libreoffice-wiki-publisher but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Comment est-ce que je peux faire??? MERCI pour votre aide.

d’après How do I re-install LibreOffice? [solved] - Linux Mint Forums
il faudrait aussi

sudo apt-get remove --purge libreoffice*
sudo apt-get clean
sudo apt-get autoremove

Bonjour,
pour trouver tous les fichiers installés, saisir

apt list libreoffice* --installed

Vous obtiendrez une longue liste.

Les paquets .deb fournis par LibreOffice sont nommés avec ajout du numéro de version

libreoffice7.5…

Par suite, si on veut désinstaller une version en particulier, penser à ajouter ce numéro dans le nom des paquets.

Sur ma machine, tout est un peu mélangé, avec des restes de l’installation par défaut, marqués comme suit :

 [installé, automatique]

Les lignes des versions installées par moi-même se terminent par :

[installé, local]

Les commandes mentionnées par @fpy sont super, merci !

Je ferai le ménage quand je saurai faire.