Can we create one certificate manually on Cloudflare dashboard and this role picks that instead of creating new certificates every time? about trellis-cloudflare-origin-ca HOT 1 CLOSED

This role makes 1 origin certificate per site on each web server. Generating origin certificate is fast and free, I don't think reusing them on multiple sites adds any benefits.

This example generates 1 origin certificate (on each web server) for all 4 domains.

wordpress_sites:
  example.com:
    site_hosts:
      - canonical: example.com
        redirects:
          - ww1.example.com
          - ww2.example.com
          - ww3.example.com
    cloudflare_origin_ca:
      hostnames:
        - example.com
        - '*.example.com'

This example generates 2 origin certificates (on each web server), 1 for each site.

wordpress_sites:
  example.com:
    site_hosts:
      - canonical: example.com
        redirects:
          - ww1.example.com
          - ww2.example.com
          - ww3.example.com
    cloudflare_origin_ca:
      hostnames:
        - example.com
        - '*.example.com'


  xxx.example.com:
    site_hosts:
      - canonical: xxx.example.com
        redirects:
          - xx1.example.com
          - xx2.example.com
          - xx3.example.com
    cloudflare_origin_ca:
      hostnames:
        - '*.example.com'

Is it not possible that we create one origin certificate defining example.com and *.example.com from the dashboard and this plugin picks that instead of creating a new one every time?

Not possible and not intended to.
If you must, use https://roots.io/trellis/docs/ssl/#manual

what exactly triggered the new certificates

During provision, if {{ nginx_ssl_path }}/cloudflare-origin-ca/{{ item.key }}.XXX is absent, this role generates new certificates.

Does Cloudflare limit the number of origin certificates creation?

Ask Cloudflare support. I haven't bump into any limiation.

And if by any chance referencing an old manually created certificate is possible, and if that would help.

If you must, use https://roots.io/trellis/docs/ssl/#manual

Learn more on https://discourse.roots.io/t/site-on-trellis-provisioned-do-droplet-subdom-site-on-2nd-droplet-cloudflare-oc/14516/6

from trellis-cloudflare-origin-ca.