How to get more disk space ? i.e. what can be removed without breakings?

I suspect that my old Yunohost install has left unused files from places to places. Some are easy to guess, like Yunohost backups, cache and old logs, but there is a lot more. I’ve browsed some documentation, but still I’m not sure.
May be one can help ?
There is a big and old Yarn cache directory in /usr/local/share/.cache/yarn. I know that cacher can be deleted, but is this one used for YH operations or only npm ? in first case, can it be deleted without slowing YH operations ? Else, can it be purged from unused files ?
There is also a node JS directory in /usr/local/n/versions which looks redundant (for me) with /opt/node_n/n/versions.
Is there other places I missed ?
Thanks in advance.
(vous pouvez répondre en français)

Sorry I have forgotten to add that Yunohost version is 11.1.20

Did you think of the yarn cache in each node application too (in /var/www)? Same for logs?

No I didn’t, but a quick search doesn’t show any cache files.
Anyway, thanks for the idea.

What quick search did you do?
For some apps it would be in .cache/yarn for example and would not appear is du searches.