Maybe this works with Nextcloud and ClamAv....
https://forum.cloudron.io/topic/12551/humhub-virus-scanner-module-compatibility#:~:text=With this working%2C i think it would also work for other apps like Nextcloud%2C i guess%3Fld also work for other apps like Nextcloud%2C i guess%3F
Not tested with Nextcloud, but maybe it's worth trying?
I remember something like a ClamAv plugin?
https://github.com/nextcloud/files_antivirus?tab=readme-ov-file
Install that and let it run with the ClamAv in a separate VM