What should contents of data directory be?

After upgrading from owncloud to nextcloud I was looking though my data directory (located outside of my web root) and I’m wondering if there are old owncloud files in there I can delete. The contents of my data directory are presently:

files_external (has rootcerts.crt in it. Am I supposed to mount external storage here?)
.htaccess (I know this is required)
htaccesstest.txt
index.html
mount.json (I think I read somewhere that this was going away?)
.ocdata
owncloud.db
updater_backup
And of course the various user directories.

Thanks.

No, nothing you should delete directly from the data dir

@nickvergessen User is probably asking, because the mount.json did break his external storage:

Well, I thought I had fixed it but apparently removing the mount.json didn’t fix anything. So I put it back. Thanks of the response though.
Currently trying to make a new external storage directory to see how that goes. It may just be a problem with the mac owncloud client. I tried installing the new nextcloud one but ran into the same errors others are having with running TLSv1.2 and the client.

Perhaps it is better, to gather all the information and to create a bugreport on github.