Drupal 8.x

I'm trying to upgrade a simple Drupal 8.9.20 site to Drupal 9 so I can get to 10.  I followed these instructions but when I run composer update I get this.

Would love to download a version of the Group Domain module compatible with Drupal 8, but can't find it..where do I go?

I first banally launched a composer update that miserably failed with some incompatibility.

Problem 1
    - drupal-composer/drupal-scaffold[2.5.0, ..., 2.6.1] require composer-plugin-api ^1.0.0 -> found composer-plugin-api[2.2.0] but it does not match the constraint.
    - Root composer.json requires drupal-composer/drupal-scaffold ^2.5 -> satisfiable by drupal-composer/drupal-scaffold[2.5.0, ..., 2.6.1].

Then I tried to follow the documentation at the URLs below.

Hi- Hoping someone can help!

I'm trying to upgrade a Drupal 8.8.1 site, eventually to D9, but initially to 8.8.4 (which I read somewhere is a needed waypoint for some module). After backing up and manually moving the new core+ files in place, it crashes with the error "'CommerceGuys\Addressing\AddressInterface' not found". Addressing is a library required for the Address module, which is required for Commerce, etc.

According to the Address module info, manual installation isn't possible, so I tried using Composer to reinstall/upgrade Address, but I'm getting this error:

Hello,

I have been away from dealings with Drupal for some time but now landed with a task of setting up Drupal with Elasticsearch.

Druapl is v8 and Elasticsearch Connector v7. Elasticsearch v7.xx is running on the same machine.

Good morning, all.

A few weeks ago, when I logged into my Drupal intranet site, I got a browser full of gibberish starting with "The website encountered an unexpected error. Please try again later."