Is there a reason that the Tasks doesn’t work for you? You can make Tasks in the Calendar app and they appear inline with other events, and notifications work as you describe them from what I can tell

The most important part of reminders for me was the way they worked, by putting up a notification that didn’t go away until manually dismissed. Very useful for important stuff like taking a medicine.

This is exactly how the Tasks feature works. I use it for this exact purpose and it works well for me.

Simple Calendar Pro and Etar are both available on F-Droid and have CalDAV support. Simple Calendar Pro distinguishes between “events” and “tasks”. Etar does not have that distinction as far as I know but I’ve used it for reminders by creating 0 minute long " events".

I’ve honestly been using Microsoft Todo for a while anyway since it’s way more feature complete and also allows both reminder dates and due dates.

Google Keep still uses reminders. I’m not sure how long it will last, since they were already removed from the Calendar app.

Tasks work pretty much the same though.

I use the blackberry apps with the calender and the notifications stay up unless you dismiss or hit repeat. Syncs with basically all calendar/email systems and works well with google calendars but I haven’t tried anything self-hosted (it seems like it should work, you would just put in the settings manually).

I’ve taken to DIY-ing things like this using Tasker simply because it’s the most reliable long-term solution: whatever trigger I want with whatever notification options I want and it never stops working. Plus, triggers can be dynamic and notifications can be set to be undismissible by swiping¹.

What I’d recommend that you try (as written, you only have to do the Tasker setup once and it’ll work for every event you do the calendar setup for):

• (calendar side) set up a calendar event for what you want a task for, have the title start with a prefix of some sort (short, and ideally one that won’t occur naturally, so something like [tsk] (note the lack of vowel: ensures that it can’t be matched accidentally by an actual calendar event. Ditto for the square brackets))
• (calendar side) make sure it sends a notification for when you want to be reminded. Pretty sure that you are forced to use the 10 min notification option that’s there by default (I’ve never managed to remove or change that one, but I digress) so add another if you need to.
• (tasker side from this step onwards) create a new named task that uses the AutoNotification plugin to dismiss the calendar event notification with that prefix, then switch over to the profiles list (we’ll come back to this)
• create a new event profile using the AutoNotification plugin and configure it to intercept every notification with that prefix in the title and from the Calendar app (by matching on the app in addition to the prefix, you don’t need to figure out how to remove the prefix from the title later on. I mean, you can, but you don’t have to)
• when it asks for a task to use, choose the one you created earlier
• go back to the task you created, then start having fun!

From there, you could have tasker post a notification with the event’s title, configured as persistent, with a button in it to dismiss it. Or make a long beeping sound. Or open an app. Or etc etc.

¹ aka “persistent”, but that’s a bit ambiguous in context. What does persistence mean here? Does it come back after swiping it away (you could do that, but it’s extra work)? can you swipe it away? Etc

I really like using Tasks over Reminders because of reoccurring events and subtasks