Theme development

I installed the Twig Tweak module on my site to render Views on the home page.

I want to make the display mode frontpage_tasks for the current user, his account, his stores and his groups.

{{ drupal_entity('user', user.id, 'frontpage_tasks') }}
{{ drupal_view('accueil_page_liste_des_taches_boutique', 'block_1') }}
{{ drupal_view('accueil_page_liste_des_taches_groupe', 'block_1') }}

Here is one of my Views :

Hello,

I just installed a Drupal sub-theme via CDN. Now, the first thing I'd like to do is to install a carousel on the front / home page.

I'm not sure how to do this..

I've looked at the official Bootstrap site (https://getbootstrap.com/docs/5.0/components/carousel/) and that leads me to 3 questions:

1) I have Drupal 9 and Bootstrap 3 installed. This website (link above) is for Bootstrap 5. Should I be referring to this website?

In the menu at the top left of my site, I have accordion menu.

I want to rotate the "+" icon when the accordion is open.

In the green buttons, at the top of the menu, I want to make a roration of the "^" icon when the accordion is open.

The rotation works, but the icons do the rotation, even though I didn't click on the accordion.

Why is it not working properly ? What is wrong with my CSS ?

https://dev.s1biose.com/fr

I read the following on Drupal on Sub-Theming:

You should never modify any theme or sub-theme that is packaged and released from Drupal.org, such as Drupal Bootstrap. If you do, all changes you have made will be lost once that theme is updated. Instead, you should create a sub-theme from one of the provided starterkits (this is considered a best practice). Once you've done that, you can override CSS, templates, and theme processing.

My question is the following:

Hello, I am totally new to Drupal and have a couple of questions:

1) Should I be installing Drupal 8 or Drupal 9?

2) If I install Drupal 9 (assuming I'm going with 9 since it is the latest version), should I install Bootstrap 3 or Bootstrap 4?

3) What are some of the best free themes for Drupal 9? I've searched on the web but everything seems to refer to Drupal 7 or 8..

Thank you!!

Hello everybody .

I have a content type motorcycles . In that a Term reference field  for the brand  of the motorcycle .

I have a made a page view ( exposed form in block )  to search for a particular brand of a motorcycle . In FILTER CRITERIA i have an exposed filters using simple hierarchical select ( content:has taxonomy terms ( with depth ;simple hierarchical select (exposed ) .So that works fine , a dropdown menu shows with the vocabulary terms of the brands and types .