you need to downgrade your install
change the respository yo "linuxserver/nextcloud:140" and it will downgrade it.
then you will need to manually upgrade next cloud to v13 and then remove the ":140" part and upgrade and you will be fine.
i did that lastest update and I just got a php is not compatable error so I downgraded NC to 140 and now I can not login with any username or password. it just times out and gives mie a blank browser screen.
i am running maria as my DB