I’m having the same problem right now. I tested the default theme and all plugins (including rank math) disabled. The problem continues anyway. Woocommerce account cart and payment pages marked noindex.
myaccount, cart and checkout pages are usually set to noindex by default.
In your site, the plugin WooCommerce One Page Shopping displays cart and checkout pages on product page which is likely the reason they are being marked as noindex. You will note if you disable the one page shopping plugin, the product are back to indexed. Could you please check and let us know.
I couldn’t reproduce this issue on my setup with only Rank Math, WooCommerce & WooCommerce One Page Shopping plugin. So it looks like one of the 78 plugins active on your site is conflicting with Rank Math.
From the screencast you shared, it’s not clear which plugin is conflicting with the Rank Math plugin as there were few other plugins active when you were troubleshooting the issue. As there are 78 plugins active on your site, please enable troubleshooting mode and activate Rank Math & WooCommerce plugin. After that try enabling other plugins one by one till you find the culprit.
Please let us know if you find the plugin conflicting with Rank Math so we can further debug this issue.