Power Automate flows have an option called Run only users to specify in whose context the flow will run.
You can have basic Microsoft licenses for all employees in the organization. If your flow is not using premium connectors or actions, the flow can be triggered by any user in the org.
But if your flow is using premium actions or connectors — instead of buying a premium license for all employees, you can buy premium licenses for just a few service accounts and make them the owner of the flow.
This option is available only for instant flows — meaning the flow must be triggered from Power Automate or Power Apps.
Also remember: the flow runs under the service account's context. So if you have a premium connector that sends an email, the email will be sent from that service account — not from the user who triggered the flow. If you need to send email from the triggering user, this workaround won't work for that connector.