Hi @lhh995 ,
Welcome to our forum.
Considering the issue only occurred after you install the Windows updates, I'm afraid these Windows updates that you installed recently may bring any differences that casue you couldn't change your Outlook run in win7 compatibility mode. And it's worthy mentioning that running Outlook in compatibility mode may cause some other issues, so I'm afraid it's not a long-term solution.
So, if you indeed need this feature, I'm afraid you may need to revert your windows to check. Then, based on my research, I found a similar idea in our uservoice of Outlook for Windows, it's recommended to vote it, which may increase the priority for Microsoft engineers to create a possible option or feature that can be included in the future.
Besides, if you still need further assistance, due to here we mainly focus on general issue about Outlook desktop client and your issue may be more related to windows, in order to solve your issue better, it's suggested to add any other related windows tag in your post, so that there may be more experts in windows to provide more targeted suggestions here.
If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.