I am lucky in that I haven't used Jira in many years, so here are some examples of how GitHub does it:

- create an issue: redirect to the created issue

- create an issue from a project view (kanban board): close the creation modal, stay on the view, and let the newly created issue show up in the list

- create a sub-issue from within an issue open in a side panel of project view: close the creation modal, stay on the parent issue and render the newly created sub-issue in the section called "sub-issues"

Within the awkward constraints where GitHub projects clash with the old UX of issues this is works very well and I know way beyond any reasonable doubt that the desired action has indeed been performed. Error states like failure to create an issue can be rendered in the modal and I can retry right in context too. I fail to see how toasts would add anything.

In a product based on different principles this might not be possible but then the GitHub doc is internal guidance and not a universal rule.

As an aside, GitHub's issue creation modal used in the project view is well executed.