diff --git a/js&css/extension/www.youtube.com/appearance/details/details.css b/js&css/extension/www.youtube.com/appearance/details/details.css
index db85f60fb..f76b34895 100644
--- a/js&css/extension/www.youtube.com/appearance/details/details.css
+++ b/js&css/extension/www.youtube.com/appearance/details/details.css
@@ -27,7 +27,9 @@ html[it-subscribe='transparent'] #subscribe-button button {background-color:rgba
 html[it-subscribe='remove_label'] #subscribe-button button .yt-spec-button-shape-next__button-text-content,
 html[it-subscribe='hidden'] #subscribe-button,
 html[it-join='remove_label'] #sponsor-button button .yt-spec-button-shape-next__button-text-content,
+html[it-join='remove_label'] ytd-sponsorships-offer-module-renderer button .yt-spec-button-shape-next__button-text-content,
 html[it-join='hidden'] #sponsor-button,
+html[it-join='hidden'] ytd-sponsorships-offer-module-renderer,
 html[it-purchase='remove_label'] #purchase-button button .yt-spec-button-shape-next__button-text-content,
 html[it-purchase='hidden'] #purchase-button,
 html[it-youtubeDetailButtons='remove_labels'] #menu button div:nth-child(2), 
diff --git a/tests/unit/join-button-hiding.test.js b/tests/unit/join-button-hiding.test.js
new file mode 100644
index 000000000..0541ec80c
--- /dev/null
+++ b/tests/unit/join-button-hiding.test.js
@@ -0,0 +1,29 @@
+// Test for Issue #3669: Join button not hiding when set to Hidden
+
+const fs = require('fs');
+const path = require('path');
+
+describe('Join Button Hiding (#3669)', () => {
+	let detailsCssContent;
+
+	beforeAll(() => {
+		const filePath = path.join(__dirname, '../../js&css/extension/www.youtube.com/appearance/details/details.css');
+		detailsCssContent = fs.readFileSync(filePath, 'utf8');
+	});
+
+	test('should hide legacy #sponsor-button', () => {
+		expect(detailsCssContent).toContain("html[it-join='hidden'] #sponsor-button");
+	});
+
+	test('should hide new ytd-sponsorships-offer-module-renderer', () => {
+		expect(detailsCssContent).toContain("html[it-join='hidden'] ytd-sponsorships-offer-module-renderer");
+	});
+
+	test('should remove label from legacy #sponsor-button', () => {
+		expect(detailsCssContent).toContain("html[it-join='remove_label'] #sponsor-button button .yt-spec-button-shape-next__button-text-content");
+	});
+
+	test('should remove label from new sponsorships renderer', () => {
+		expect(detailsCssContent).toContain("html[it-join='remove_label'] ytd-sponsorships-offer-module-renderer button .yt-spec-button-shape-next__button-text-content");
+	});
+});