On a development site, we ran the process of deactivating plugins one by one, whilst keeping Woocommerce 7.7.0 active.
We found that when the WooCommerce Attribute Swatches by Iconic plugin (version 1.14.2) was deactivated, the save attribute button functionality works again, and when we re-activated it, the problem came back.
@eltucu do you perhaps have this attribute swatch plugin installed too? If so, perhaps we’ve solved the issue and it’s a clash between the latest version of WooCommerce, and the Iconic Attribute plugin.