Hi @ikako ika ,
You can send Birthday Wishes Using Power Automate.
1.To work with Power Automate in SharePoint server 2019, we need to install on-premises gateways and connect to Power Automate cloud then implement the solutions.
For more information on setting up and configuring on-premises data gateway, see:
https://learn.microsoft.com/en-us/power-automate/gateway-reference
https://www.cloudsecuritea.com/2018/10/using-on-premises-data-gateway-with-sharepoint-2019-and-microsoft-flow/
2.Inside the list create there columns as follows:

3.For specific power automate flow steps, please refer to this article:
https://medium.com/@swathymothilal95/birthday-wishes-microsoft-power-automate-912ad998c15c
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