you can create a site workflow using sharepoint designer and we can make this to work like timer job.
- Your complete workflow look like in below image
2. in this step you know how to initialize workflow variable to call rest api list along with fields, you can specify more fields with comma separated to get them
3. build the dictionary variable for accept, content type
4. Call http service in app step(this app step used to run the service call admin privileges
5. see the call http service action properties and mention them as in the image
finally retrieving the birthday list using for loop and sending email if birthday is today
once you created the workflow Save and publish the workflow
now go to site workflows on the site and start the workflow manually and it will start and run like timer job.