Tasks.org (from fdroid) works with WebDAV for free (you should still donate though if you adopt it). Have been using it for the better part of the past two years for calendar, tasks, contacts. For notes and documents - Nextcloud. Haven't had one issue. Don't know what OS you use - but CalyxOS have a feature where you can backup all your apps to nextcloud/local storage and restore them on a new phone .

I've used tasks with my own nextcloud account and davx5, it didn't require any payment to sync, so maybe the payment is when syncing with the tasks.org service?

Nextcloud has lots of "apps" which you can install and enable if you own the server. Tasks is one of them. For RSS feeds, I use the News nextcloud app. For podcasts, i use antennapod, don't listen to many podcasts. Pretty sure you can use the nextcloud news app to keep track of those via rss, but never tried that myself. For notes, I just use the nextcloud notes app.

File syncing: Nextcloud has that baked in. On mobile, I use the official nextcloud app. On desktop, I use their app to keep my Documents folder, Videos and Photos synced. Just as you would with google drive or microsoft one drive. I use keepass for my passwords, so I have the file on my nextcloud account. That is synced to all of my devices, so I can access it at any time and it's always updated if I change anything.

I also use cospend to keep track of expenditures in the household together with my wife. There's also Deck for kanban board like tasks which syncs with your calendar. Carnet for a google keep alternative. And bookmarks, which allows me to never have to sign in to firefox, and have my bookmarks synced by using the floccus extension.

Open source apps will oftenly have missing features when compared to their corporate made counterparts. I find the tradeoff between a few features but control over your data and lack of advertising completely worth it. The major downside in my opinion is that to get all of this open ecosystem setup you need a fair amount of technical knowledge. That's a major threshold for many people.

I manage to make use of nextcloud as a replacement for all google / microsoft services, and it's costing me €4 / month, with 300gb of storage on my vps.