Hey @iuri1, welcome to the Nextcloud community and thanks for supporting Nextcloud snap 
Sorry to hear you are having issues with your Nextcloud snap installation. If you’ve come this far, you’re on the right track! There is a good chance someone in the community has had a similar issue and knows how to resolve it.
Below are some links to how-to’s answering frequently asked questions and may help you help yourself;
- How to install Nextcloud snap
- How to configure Nextcloud snap
- How to edit config.php for Nextcloud snap
- How to use OCC management console for Nextcloud snap
- How to revert Nextcloud snap after failed update
- How to manage failed automatic update in Nextcloud snap
- Nextcloud snap wiki and support
pay special attention to:
- Requirements especially OS Requirements
I need the mysql and other system data to be elsewhere because my /var gets erased at reboot and snapd/snapctl doesn’t seem to offer a way to configure this
simple answer, nope snapd/snapctl will not offer this see Data locations - Snap documentation and see Snap Confinement
system data to be elsewhere because my /var gets erased at reboot
this is obviously your issue and to my knowledge /var is in no way relevant for the snap! please be absolutely clear about this.