use helper to check of variant is invariant

src/Umbraco.Web.UI.Client/src/packages/core/property/property/property.context.ts

@@ -112,7 +112,7 @@ export class UmbPropertyContext<ValueType = any> extends UmbContextBase<UmbPrope
 
 		this.observe(this.#datasetContext.currentVariantCultureIsReadOnly, (value) => {
 			// always allow invariant properties to be editable
-			const isInvariant = !this.#variantId?.getValue()?.culture;
+			const isInvariant = this.#variantId?.getValue()?.isInvariant();
 
 			// always allow editing invariant properties
 			if (isInvariant) {