Don't know about Gnome Tasks, but if you got a Nextcloud account somewhere, then you get quite a simple UI for your events and tasks with Kalendar.
KDE
KDE is an international technology team creating user-friendly free and open source software for desktop and portable computing. KDE’s software runs on GNU/Linux, BSD and other operating systems, including Windows.
Plasma 6 Bugs
If you encounter a bug, proceed to https://bugs.kde.org, check whether it has been reported.
If it hasn't, report it yourself.
PLEASE THINK CAREFULLY BEFORE POSTING HERE.
Developers do not look for reports on social media, so they will not see it and all it does is clutter up the feed.
Kalendar allow syncing events from various sources e.g. Nextcloud or any DAV service. I think this should also work with google tasks but I'm not 100% sure (event and tasks are different api with the google api)
Kalender works fine. I expected not seeing sub-tasks but glad to see it. It exceeded my expectations a bit
I use Thunderbird for this, it syncs with Google Tasks. It's a bit janky but works. Here's a screenshot of how it looked 4 years ago (not much has changed) https://www.ghacks.net/wp-content/uploads/2019/10/Manage-your-Todo.txt-with-Thunderbird-using-this-extension.jpg
It's been a while since I set it up but I think it starts working automatically when you connect your Google Calendar to the Calendar in Thunderbird.