docs: create v21 announcement article

[markwhitfeld]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngxs/store/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] Other... Please describe:

Other information

Initial article generated using Claude, with the following prompt:

Create an "Announcing NGXS v20" article in the #file:publication  folder.
Examine the #file:CHANGELOG.md  to see what the changes were and if needed, take a look at the changes made in the commits between the v20_1 branch and the v21_0 branch to understand what was changed.
Please ensure that the article is broken down into the sections highlighted in the
#file:announcement_template.md and is of similar tone and form to the #file:article.md .
It is ok to expand on a new feature by looking at what was written about the feature
in the documentation or the corresponding pull request.
#codebase 

[nx-cloud]

View your CI Pipeline Execution ↗ for commit 6d4210d

Command	Status	Duration	Result
nx run-many --target=test --all --configuration...	✅ Succeeded	1m 21s	View ↗
nx run-many --target=lint --all --configuration...	✅ Succeeded	5s	View ↗
nx lint-types store	✅ Succeeded	<1s	View ↗
nx run-many --target=build --all	✅ Succeeded	3s	View ↗

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☁️ Nx Cloud last updated this comment at 2025-12-17 20:27:50 UTC

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commit: 6d4210d

[bundlemon]

BundleMon

Unchanged files (6)

Status	Path	Size	Limits
✅	fesm2022/ngxs-store.mjs	104.15KB	105KB / +0.5%
✅	fesm2022/ngxs-store-internals.mjs	13.62KB	15KB / +0.5%
✅	fesm2022/ngxs-store-internals-testing.mjs	10.32KB	13KB / +0.5%
✅	fesm2022/ngxs-store-operators.mjs	6.05KB	7KB / +0.5%
✅	fesm2022/ngxs-store-plugins.mjs	2.37KB	3KB / +0.5%
✅	fesm2022/ngxs-store-experimental.mjs	574B	2KB / +0.5%

No change in files bundle size

Unchanged groups (1)

Status	Path	Size	Limits
✅	@ngxs/store(fesm2022)[gzip] ./fesm2022/*.mjs	33.62KB	+1%

Final result: ✅

View report in BundleMon website ➡️

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Current branch size history | Target branch size history

[bundlemon]

BundleMon (NGXS Plugins)

Unchanged files (9)

Status	Path	Size	Limits
✅	Plugins(fesm2022)[gzip] storage-plugin/fesm2022/ngxs-storage-plugin.m js	4.05KB	+0.5%
✅	Plugins(fesm2022)[gzip] router-plugin/fesm2022/ngxs-router-plugin.mjs	3.4KB	+0.5%
✅	Plugins(fesm2022)[gzip] hmr-plugin/fesm2022/ngxs-hmr-plugin.mjs	2.72KB	+0.5%
✅	Plugins(fesm2022)[gzip] websocket-plugin/fesm2022/ngxs-websocket-plug in.mjs	2.58KB	+0.5%
✅	Plugins(fesm2022)[gzip] form-plugin/fesm2022/ngxs-form-plugin.mjs	2.47KB	+0.5%
✅	Plugins(fesm2022)[gzip] devtools-plugin/fesm2022/ngxs-devtools-plugin .mjs	2.23KB	+0.5%
✅	Plugins(fesm2022)[gzip] logger-plugin/fesm2022/ngxs-logger-plugin.mjs	2.03KB	+0.5%
✅	Plugins(fesm2022)[gzip] storage-plugin/fesm2022/ngxs-storage-plugin-i nternals.mjs	947B	+0.5%
✅	Plugins(fesm2022)[gzip] router-plugin/fesm2022/ngxs-router-plugin-int ernals.mjs	453B	+0.5%

No change in files bundle size

Unchanged groups (1)

Status	Path	Size	Limits
✅	All Plugins(fesm2022)[gzip] ./-plugin/fesm2022/.mjs	20.85KB	+0.5%

Final result: ✅

View report in BundleMon website ➡️

---

Current branch size history | Target branch size history

[bundlemon]

BundleMon (Integration Projects)

Unchanged files (1)

Status	Path	Size	Limits
✅	Main bundles(Gzip) hello-world-ng21/dist-integration/browser/mai n-(hash).js	67.19KB	+1%

No change in files bundle size

Final result: ✅

View report in BundleMon website ➡️

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Current branch size history | Target branch size history