Hello @AKira Kawahara , welcome to the Microsoft Q&A forum.
I am not familiar with the language from the screenshot, so I might have missed some details. As per my understanding of the question, you have deployed a VPN gateway and if you are changing any settings for this Gateway notification and logs shows as successful but on the Overview screen of VPN Gateway you get an error saying update failed. When you are creating a VPN connection you are getting an "Unexpected Error" and this configuration worked 2 months ago.
If my understanding is correct, this issue may be due to a transient portal error, to pinpoint this issue you can you run below PowerShell command? and validate if the setting you had configured is present or not.
Get-AzVirtualNetworkGateway -Name <VpnGatewayName> -ResourceGroup <ResourceGroup>
If the setting is not present, can you try and add the setting via Azure PowerShell commands and see if you are getting any errors. You can also try and create a new connection using this PowerShell command.
If the setting is present, it should be a Portal error. In this case, it will be better if you could file a support case. Please make sure to capture the browser trace as it will help debug this issue. If you do not have a support plan, please refer to my private message below. (Please let me know if you are unable to see the private message) Thank you!