Version 2.0

@matia.ward, I decided to add breadcrumb into Decoupled Kit Block (2.0.3 version).
Please, see system_breadcrumb_block block and settings/breadcrumb section in the resulted JSON.

Not sure if I'm doing something wrong, but it seems to give back the same breadcrumbs regardless of what the custom_path string is:

"settings": {
          "id": "system_breadcrumb_block",
          "label": "Breadcrumbs",
          "label_display": "0",
          "provider": "system",
          "breadcrumb": [
            {
              "text": "Home",
              "url": "/"
            },
            {
              "text": "Jsonapi",
              "url": "/jsonapi"
            }
          ]
        },

The breadcrumb output should change based on that variable, correct? Example URL string (whitelisted IPs only, so you won't be able to view the JSON): https://drupal.nidentistry.devsr.com/jsonapi/decoupled_kit/blocks?curren...

@matia.ward, ah, sorry, you are right. Core breadcrumb doesn't know how to construct breadcrumb correctly (it uses $this->context->getPathInfo() istead of $route_match data). Try to use Easy breadcrumb → or similar modules.

@matia.ward, I did commit to dev version, please check.

I updated a site to the 2.0 dev version and looked at the json response using this url: /jsonapi/decoupled_kit/blocks?current_path=/testimonials/single-post&current_theme=gin. My response now includes the parent page! The indexing is off though, goes from 0 then 2:

"drupal_internal__id": "gin_breadcrumbs",
        "theme": "gin",
        "region": "breadcrumb",
        "weight": 0,
        "provider": null,
        "plugin": "system_breadcrumb_block",
        "settings": {
          "id": "system_breadcrumb_block",
          "label": "Breadcrumbs",
          "label_display": "0",
          "provider": "system",
          "breadcrumb": {
            "0": {
              "text": "Home",
              "url": "/"
            },
            "2": {
              "text": "Testimonials",
              "url": "/testimonials"
            }
          }
        },

Tested with another nested child and got even more index weirdness, lol. This path was /testimonials/single-post/another-child.

"breadcrumb": {
            "0": {
              "text": "Home",
              "url": "/"
            },
            "2": {
              "text": "Single Post",
              "url": "/testimonials/single-post"
            },
            "3": {
              "text": "Testimonials",
              "url": "/testimonials"
            }
          }

I think just fixing up the indexing would do it! Thank you!

@matia.ward, many thanks for your testing.
I've fixed that case, please test it on the dev version.
But the right way is to use contributed breadrumb modules like Easy breadcrumb → .

Thanks! So am I good to just say on the 1.x version since it seems to be getting updates as well, or will 1.x go away at some point and we should anticipate having to switch over to 2.x at some point?

Yes, of course, version 1 will be updated. Version 2 is a different approach - using system breadcrumbs instead of subdomain breadcrumbs.