You can use Copy-PnpFile to do so. It copies a file or folder to a different location. This location can be within the same document library, same site, same site collection or even to another site collection on the same tenant. Currently there is a 200MB file size limit for the file or folder to be copied.
If you have not tried Pnp before, remember to install the module first.
Here is a demo works in my end.
#Copy File to Another Site
$sourceSiteURL="SourceSiteURL"
$UserName="Account"
$Password = "PWD"
$SourceURL="Shared Documents/folder"
$TargetURL="/sites/<siteName>/Shared Documents"
$SecurePassword = ConvertTo-SecureString -String $Password -AsPlainText -Force
$Cred = New-Object -TypeName System.Management.Automation.PSCredential -argumentlist $UserName, $SecurePassword
#Connect to PNP Online
Connect-PnPOnline -Url $sourceSiteURL -Credentials $Cred
Copy-PnPFile -SourceUrl $SourceURL -TargetUrl $TargetURL -OverwriteIfAlreadyExists