Welcome to the community! Please be sure to take a look at the sticky thread at the top of the forum. Here’s a direct link:

Using Get-* Cmdlets is generally fairly safe, but Set-, Remove- can be a resume generating event. Since it’s your second day with PowerShell, I recommend taking it slowly and using extreme caution. Most Cmdlets support the -WhatIf Parameter. That’s useful so you can see what changes will be made before you make them. Nothing is more fun than deleting all of your users instead of just one due to a bad filter. Specifically regarding Active Directory, most online place will recommend using -Properties *, but it’s bad practice as it returns all properties of all users and can cause a strain if you have a large environment. It’s best to get into the practice of only requesting the properties you need.

Get-ADUser -Filter {....} -Properties Manager

You actually use it in your first of 3 Get-ADUser commands.

Here’s a thread that discusses the same thing you’re trying to do How to list a direct reports in Powershell