Add notices about classic project creation limitations (github#29062)

Author: guntrip

content/issues/organizing-your-work-with-project-boards/managing-project-boards/creating-a-project-board.md

@@ -34,6 +34,8 @@ You can also configure workflow automations to keep your project board in sync w
 
 ## Creating a user-owned project board
 
+{% data reusables.projects.classic-project-creation %}
+
 {% data reusables.profile.access_profile %}
 2. On the top of your profile page, in the main navigation, click {% octicon "project" aria-label="The project board icon" %} **Projects**.
 ![Project tab](/assets/images/help/projects/user-projects-tab.png)
@@ -54,6 +56,8 @@ You can also configure workflow automations to keep your project board in sync w
 
 ## Creating an organization-wide project board
 
+{% data reusables.projects.classic-project-creation %}
+
 {% data reusables.profile.access_org %}
 {% data reusables.user-settings.access_org %}
 {% data reusables.organizations.organization-wide-project %}
@@ -74,6 +78,8 @@ You can also configure workflow automations to keep your project board in sync w
 
 ## Creating a repository project board
 
+{% data reusables.projects.classic-project-creation %}
+
 {% data reusables.repositories.navigate-to-repo %}
 2. Under your repository name, click {% octicon "project" aria-label="The project board icon" %} **Projects**.
 ![Project tab](/assets/images/help/projects/repo-tabs-projects.png)

data/reusables/projects/classic-project-creation.md

@@ -0,0 +1,9 @@
+{% ifversion fpt or ghec %}
+
+{% note %}
+
+**Note:** You can only create a new classic project board for an organization, user, or repository that already has at least one classic project board. If you're unable to create a classic project board, create a beta project board instead. For more information, see "[Creating a project (beta)](/issues/trying-out-the-new-projects-experience/creating-a-project)."
+
+{% endnote %}
+
+{% endif %}

data/reusables/projects/project_boards_old.md

@@ -2,7 +2,11 @@
 
 {% note %}
 
-**Note:** Projects (beta), the all-new projects experience, is now available. For more information about projects (beta), see "[About projects (beta)](/issues/trying-out-the-new-projects-experience/about-projects)" and for information about migrating your project, see "[Migrating your project to Projects (beta)](/issues/trying-out-the-new-projects-experience/migrating-your-project)."
+**Notes:**
+
+* Projects (beta), the all-new projects experience, is now available. For more information, see "[About projects (beta)](/issues/trying-out-the-new-projects-experience/about-projects)" and "[Migrating your project to Projects (beta)](/issues/trying-out-the-new-projects-experience/migrating-your-project)."
+* You can only create a new classic project board for an organization, user, or repository that already has at least one classic project board. If you're unable to create a classic project board, create a beta project board instead.
 
 {% endnote %}
+
 {% endif %}

data/reusables/projects/projects-api.md

@@ -1,7 +1,10 @@
 {% ifversion fpt or ghec %}
 {% note %}
 
-**Note:** This API only applies to project boards. Projects (beta) can be managed with the GraphQL API. For more information, see "[Using the API to manage projects (beta)](/issues/trying-out-the-new-projects-experience/using-the-api-to-manage-projects)."
+**Notes:** 
+
+* This API only applies to project boards. Projects (beta) can be managed with the GraphQL API. For more information, see "[Using the API to manage projects (beta)](/issues/trying-out-the-new-projects-experience/using-the-api-to-manage-projects)."
+* You can only create a new classic project board for an organization, user, or repository that already has at least one classic project board.
 
 {% endnote %}
 {% endif %}