Session expired (error 419) on Safari 12.1.2 after updating to Laravel 7

After updating an existing project to Laravel 7, logins suddenly stopped working on Safari (12.1.2 on Mojave 10.14.6). Chrome (80.0.3987.122), on the other hand, would work as expected.

After a couple of hours of literally wasted time trying to figure out what could be behind this, it turned out to be related to the same_site setting on the sessions.php config file; on the Laravel 7 upgrade guide, it's written that we should, and I quote:

"

Next, please update your session configuration file's secure option to have a fallback value of null and the same_site option to have a fallback value of lax:

'secure' => env('SESSION_SECURE_COOKIE', null),

'same_site' => 'lax',

Reverting same_site to null, however, made things work again on Safari. Is this a bug, an issue on my end, a little bit of both?…