A quick search through the community, and there aren’t many posts about this, so just in case someone doesn’t know about this: You can access your nextcloud using an Android phone via the Solid Explorer App.
By using the “connect to Owncloud” function.
in ES explorer you can do that too via ftp>webdav or with total commander with the webdav addon.
This may be too late, but you can use the owncloud option but in nextcloud, set an application password and use that instead. Works for me.