I opened this issue on RCMCardDAV GitHub repo thinking it was a bug of them, while it turned out it was just ignorance (on my side).
TL;DR:
To make a long story short, if you want to sync groups of contacts, using a CardDAV address book, make sure that every client/sync application is using the same format to store groups. This applies to e.g. roundcube, with the plugin of this post's link, DAVx^5 sync app, and generally each client which supports CardDAV.
- rcmcarddav settings in roundcube

- DAVx^5 settings (it's in Italian, sorry. The difference between group types is the same as above though)

Before setting DAVx^5 to the correct option, groups created on roundcube won't sync correctly to my phone, while the other way around worked fine.
Continuing from the previous article..
Today while trying to install yet another plugin (Calendar this time), I had a lil incident and destroyed everything 😃
Some hours later I restored a backup and we're up again. BUT! In the process I discovered some SQL errors which I believe were there since a lot ago, always gone unseen.
To make a long story short, I had to disable the standard "Personal Address Book" for everyone, because it was impossible to save any contact in there anyway.. And we are now relying on CardDAV, which is way better.
At one point I had the Calendar plugin working too, alongside CardDAV, but I had (wrongfully) installed it as a local one, so no sync to the cloud with CalDAV; it was later that I tried the CalDAV way by changing the config and shit got me.
Now I asked the people of libera.chat about the plugin, to see if it really supports any CalDAV implementation or not - and then I'll try again :) Feel free to check it out and leave a comment if you know better than me..
https://git.kolab.org/diffusion/RPK/browse/master/plugins/calendar/
and here's the configuration: https://git.kolab.org/diffusion/RPK/browse/master/plugins/calendar/config.inc.php.dist$28
I believe I'm done for today tho.. Looked like a full day's job.
Ooh, yes.. Was already forgetting. I also updated the services blob in my website with all the new stuff.
Hello o/
Just completed a new software installment for the "woodpeckers" webmail, powered by roundcube.
It's a plugin to manage CardDAV address books, so you can import them in your web contacts; I've tested it with "Radicale Cal/CardDAV" server and the import to roundcube was fast and easy peasy; hopefully it'll be the same for every other compatible server 😎
https://webmail.woodpeckersnest.space/
Yeah, that was all for your local news! Until next.