Can't log in to back end
This is due to the new core_version_requirement key taking the place of the core key in module.info files. Here's the change record: https://www.drupal.org/node/3070687.

A dirty hack to get around this would be to add the following to path_alias's .info file:


core: 8.x


I would do this only for the purpose of getting your site back in order, and remove the key afterwards. You are likely to run into this error, or similar, for other modules as well. I think that disabling the path_alias module, and any other troublesome modules, prior to upgrade might help.

This change record about path_alias becoming its own core module might be relevant, as well: https://www.drupal.org/node/3092086.

It's also worth mentioning that, if you have drush installed, you can get a one-time login link by running drush uli 1. You'll get a link that looks something like this: http://default/user/reset/1/1584508997/mFfBCIO2zmwKOm3Bh7l5bBwGxwMO6MVqJ6-S-cvZ-pU/login. Take the part of the URL starting with "/user" and append it to your domain name.

Ex: http://my.site.dev/user/reset/1/1584508997/mFfBCIO2zmwKOm3Bh7l5bBwGxwMO6MVqJ6-S-cvZ-pU/login