Calendar integration

[beng7]

Hi
First NICE project, I currently use a combination of Nextcloud (for CardDav (contacts, vcf format) and CalDav (calendar, ics format)), DAVx5 (for account management & synchronization), ICSx5 (for additional national holidays, moon, etc... calendarsand Note (for on the fly notes) but it means all my data is on a server i have to pay for that does not belong to me, and I feel you can never trust others completely in term of privacy, sercurity.
I am also using Syncthing and I found Decsync CC by chance actually; I am currtently trying to set it up on a brand new phone that I just got (my current phone is dying and I will eventually have to put the sim card in the new phone but already I'm setting up the new phone.
so I shared a dedicated folder in syncthing for everything that can be Decsynced.
So I went into Nexcloud and exported both my contacts and calendar and copied the files into my dedicated Decsync syncthing folder and in my contact application on android I pointed to this contact file as my default contact book and it works fine.
Now when it comes to the calendar, the integration is not as straightforward process: whether I click on the cadendar nad it tells me no account or I try to integrate it from Decsync - it cannot find the ics file in the Decsync folder

Can you please clarify how I can integrate the ics calendar into decsync - what are the different necessary steps please?
Oh, and can you please also clarify which is actually the secondary "Tasks" application - who are the developers?

Now, i'm looking for a goog local note app.
Any way thanks a lot already for all your efforts, i believe you app can have a great future!