Unable to update wordpress version

Is the screen really grey? I know it more as white. Then here are possible reasons:

https://www.ads-software.com/documentation/article/common-wordpress-errors/#the-white-screen-of-death

A look at the error log would be advisable. There you should find details about the cause. Your hoster can help you find it.

its like left bar in admin area is still visible, but i don’t see any message like “Updating or unpackaging etc..” on the screen. Or any error saying it can’t be updated.

2 days ago we had an issue with a plugin (Monster Insights) and kept getting 403 error every time tried to publish or update a post because it needed to be re-authenticated. I deleted the plugin completely but still getting 403 error. Server people recommended to reinstall the plugin and re-authenticate. But I can’t install plugin because it’s not compatible with current WP version. And I am unable to update WP version.

If you get an empty grey screen instead of white, it indicates WP admin has partially loaded before some sort of error occurred. Regardless, error log entries could be informative.

If you’re getting 403 responses for files you know you or WP should have access to, you should verify file permissions via FTP. Proper permissions vary by installation, but 644 for files is typical. The file’s owner should normally be the server user that PHP and WP run as. Sometimes the server’s modSecurity or similar security measures can interfere with normal operation.

While you will want to resolve these 403 errors, you can still update WP to the latest version by doing so manually via FTP. Similarly you can install a plugin manually by uploading its files via FTP. Then activate it from the admin plugins screen.