I don't understand this problems on the KDE instance. Can we arrange a debugging session with a Nextcloud developer and an KDE sysadmin? And if yes, we should coordinate by email. Can the right contact person send me an email? Thanks

Hmm. Nextcloud Text is working fine here and at many other instances on the internet. There might be a configuration issue here. Could you create an issue here? https://github.com/nextcloud/text/issues
Thanks.