I cannot invite attendees to an event I set up

I am setting up an I select "Invite Participants" the pop-up screen locks up.

Is this on a local calendar or a synced one with google or the like. Or go forbid one on outlook.com with an addon to enable the calendar function.

The pop up locks up for how long?

I have tried to change accounts one at the time with no luck.

This I do not understand. Do you mean you have tried to add the even to different calendars?

I also selected the "Attendees" tab near the bottom of the pop-up. That did not help either.

That adds nothing, only displaying those that have been invited. There is a right click menu that will display the same invite dialog as the toolbar button, but as the same dialog, I would expect it to behave exactly the same.

Do you have address book contents for the auto-fill feature to draw on when adding contacts?

This is running on a Windows 11 Home operating system. Any help would be appreciated. PS - I moved from Microsoft Outlook to Thunderbird as I did not like the new Outlook. This has been very frustrating.

Thunderbird is not Outlook. Virtually nothing will be exactly the same unless it is an accident. There has been a special class of bug for the last 18 years described as outlook parity bugs, mostly submitted by folk wanting Thunderbird to have some feature they miss from Outlook. See https://bugzilla.mozilla.org/show_bug.cgi?id=423488

Is this on a local calendar or a synced one with google?...Yes, this is a Gmail.com mailbox. I can access it using the Google web tool (which I find not very user-friendly). So I assume they are linked.

This I do not understand. Do you mean you have tried to add the even to different calendars?...Yes, I am using different calendars. I try to import my Outlook calendar (which was the same email address). I could not import it because of differing formats. So I opted to export from Outlook .csv file and adjusted it to match the import requirements of Thunderbird. When I did that, Thunderbird put it into another calendar. So I have have calendars named "Home", my email address, "Holidays in United States", and one named "Complete Calendar". I tried to send from each of those which had appeared in the event dialogue drop down box.

Do you have address book contents for the auto-fill feature to draw on when adding contacts?....Often, until a week ago, I could begin to type a name in the invite box and auto complete kicked in to show me my options. I believe that is what you are talking about. I cannot get to that screen now.

Thunderbird is not Outlook… I understand this. I I did elect to go with Thunderbird because the reviews said it was similar to Outlook so I would not have to learn as much. I have been happy with it until it stopped working and I cannot originate events to which I want to invite others. That is frustrating.