Can running out of storage break nextcloud?

I am running nextclud hub 18 on digital ocean, from the snap on a digital ocean ubuntu 18.04 server. I am unable to connect to the web interface of via apps on android. I am just getting error messages. I am able to login via ssh. I can see that all the storage on dev/vda1 is used up (25GB of 25GB).

Would nextcloud allow me to upload so much that it would break nextcloud or is this unrelated?
Is it safe just to go to the data folder and delete some files?