The F-Droid version is built by the F-Droid build machine, not me, so it has a different signature. If you have the Google Play release installed then Android will only allow upgrades that are signed by me. If you uninstall the Google Play version then you should be able to install the F-Droid version

That's what I thought, but I don't have the Google Play version installed.

First I tried installing Tasks from F-Droid, but it said the thing about the signature (even if Tasks wasn't already installed). So I went to Google Play and installed it from there, then uninstalled it, cleared F-Droid's cache and rebooted my phone. Still F-Droid tells me that there is no compatible signature.

I have several other apps installed via F-Droid, and I have never encountered that message when an app isn't installed in parallel.

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edit: added missing word

That is bizarre, and now that you mention it, perhaps this is related to https://github.com/tasks/tasks/issues/971

That sounds plausible.

I once had Astrid installed, but I can't remember if it's on this phone or the previous one. But that shouldn't interfere, should it.

I had OpenTasks, that also presents itself with a icon named Tasks, but uninstalling it didn't help either.

You should be able to have all three installed at the same time

Open up your device's settings, click on apps, and make sure Tasks.org is not there. If it is, tap on it, tap on the overflow menu, and select 'Uninstall for all users'

Then try downloading an APK from https://f-droid.org/en/packages/org.tasks/ and side loading it

You can follow up with me at [email protected] if you would prefer

It's not in the lists of apps, so I can't remove it.

I'll see if I can install the APK directly.

Installing the APK directly went fine. Thanks.