Full automation of upgrading everything (full continuous-integration)

Question

I have a Drupal 8.5.x or higher website (all core, besides Redirect and Metatag).

I desire to have full automation in upgrading Drupal (core, translations, modules, themes and anything else basically) all in one go, from within Drupal GUI itself (I would prefer not to create Bash or cron scripts if I can).

Is it possible with Drupal 8.5.x or higher?

Answer 1

Is it possible to full upgrading with solely Drupal/PHP? In the sense that anything is possible given enough time/effort, yes.

Should you? Not unless you want to spend a lot of time building a bespoke, error-prone (especially if you're scoping in any modules, themes, etc.) process that will only work under the narrow scenario in which you developed it.

To get a sense of what you're asking, look at auto updates initiative. You're probably better off contributing/following the initiative instead of rolling your own.