@JohanB123 Ideally you'd use the Person column in your SP list to assign the manager to each employee. You can also use the Manager field in the user's M365 profile.
Can you clarify what you mean when you say "how to get this in my flows?".
To use the dynamic content from this column you can select the appropriate dynamic content from the dynamic content menu. When you use a person column in your SP List there will be a few dynamic content options to select from.

If you are looking for a way to send multiple SharePoint List items that have been assigned to a user in an email—check out this YT Tutorial: How to Send a SINGLE EMAIL ✉️ with multiple SharePoint list items | Build THIS Power Automate Flow
IN THIS VIDEO:
✅ How to send multiple list items in a single email with a Power Automate Flow
✅ How to create a dynamic date range
✅ How to use the Convert Time Zone action
✅ How to use a Filter Query in the Get Items action
✅ How to count number of items in an array
✅ How to use the Select action to extract a users display name and email address
✅ How to create a unique list of email addresses
✅ How to use the Create HTML Table action
✅ How to customize the HTML Table with CSS styles
✅ How to use the Send an email (V2) action
✅ How to use the Append to String Variable action
✅ How to create a custom list of items for an email
✅ How to use the Send an email (V2) action
✅ How to display singular or plural text based on the number of items returned
Hope this helps!
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