Configuring preferences and options in Outlook.com
I understand you mean actual reminder emails, not pop-up alerts. I couldn’t verify an official announcement that this email behavior has been removed, so I wouldn’t assume your previously working setup is no longer available.
Here are some suggestions you can try:
First, find an older reminder email and check its sender and subject. This will help identify whether it came from a calendar reminder, a daily agenda, or another service linked to your tasks. Keep that example for support, but don’t post your personal information here.
Next, check Junk Email and the Other inbox tab. Also review Settings > Mail > Rules and Forwarding for anything moving or redirecting these messages. If you find a reminder in Junk, select Mark as not junk.
If nothing turns up, select Help > Help in Outlook.com, search for “missing reminder emails,” then choose Still need help? > Yes. Include the older email example and when delivery stopped, and ask support to investigate the missing emails specifically.