Hi Poom Ritthirungrat1,
Good day.
Thank you for posting to the Microsoft Community. We are glad to assist.
Right click on the event Then Forward Then write the needed email .
This pearson will receive invitation with ICS file attached .

I hope this helps let me know if this is contrary to what you need, I would still be helpful to answer more of your questions .
Best Regards
Microsoft Community Moderator
Hey everyone, I figured out what they were trying to explain.
In order to get the .ics file, you need to forward the meeting invitation to another person first. Keep in mind I'm talking about a meeting invitation and not an appointment. These are the steps I followed:
- Create the event and fill out all the information.
- Invite somebody to the event. This will change the event from "appointment" to "meeting".
DO NOT INVITE YOURSELF (do not use the same email creating the event).
Any email should work.
- Once the meeting is created, the option to forward the email will be available in the right-click menu (as shown in the image above).
Forward the event to another email that can be accessed outside of Outlook, such as Gmail.
- Go to the forwarded invitation on your Gmail account. The .ics file should be attached to the email.
I know this might be too troublesome for many, and I hope the Microsoft team will solve this issue soon.
C'mon, it was so easy before