Calendar should work, and in: it syncs events, but the calendar app still needs to be made adaptive (and yes there is work in that sense).
The Nextcloud Desktop app, the one from the repos does not get credentials from GOA, you need to set it up separately and input the credentials again.
Also that app is not adaptive yet, but it can scaled to fit the screen better.
For that you can download to your Librem 5 the scale to fit script from here:
Then from the same same folder where the script is run:
bash ./scale-to-fit desktopclient.nextcloud.com.nextcloud