Drupal 8.x

I have some scripts that I need to run manually, these scripts are not meant to be ran on a regular schedule, therefore, I DO NOT want to use cron. With that, how can I kick off a php script in the background?

I've tried to use `exec` but it doesn't know what drush is, so I can't run my script that needs ran via drush.
I looked into the `Background Process` module but 1) it hasn't been updated in years and 2) it doesn't have a Drupal 8 version. 

How can I run a script in the background that isn't done through cron?

I see that in D7 tracker module was using format_interval call to render time intervals with "ago".

Now in D9 I see that it is using formatTimeDiffSince method on DateFormatter class (that in turn calls formatDiff method.

My question is what is the reason not to use formatInterval method on the same class. (which is like D7 format_interval function). I do not see any module using formatInterval method anymore. (Correct me if wrong)

My problem is I can't get Drupal 8 loaded on my local machine. All these so called easy installation routes all seem to throw an error of some kind. I've read even dev desktop has an exception for Windows 10. Currently trying Mamp and almost got to heaven(after all night and day) when this message came up.

"The website encountered an unexpected error. Please try again later.

I am looking after a Drupal 8 website for a client, but the website doesn't really rank as it should in Google.

So I'm looking for a Drupal 8/9 consultant or coach to help me improve the site with the goal to rank well.

The first steps would look as follows:
- Audit of the website by the consultant
- The consultant makes a list of actions to be taken
- Then the consultant personally coaches me through the list of actions and helps me implementing them using Teamviewer or a similar screen-sharing software