How to disable column edit function but allow API to add file

In SharePoint Online Document library, we have metadata with column 1,2,3,4. A REST API is used to add document to the columns. We want column 2,3,4 read only ( column 1 still editable). I used PnP PowerShell to make column 2,3,4 read only, as below,

$Docs= Get-PnPList -Identity Lists/ByItemID
$Number = Get-PnPField -List "ByItemID" -Identity "Number"
$Number.ReadOnlyField = $true
$Number.UpdateAndPushChanges($true)
$Docs.Context.ExecuteQuery();

but this affects REST API to add document to the columns 2,3,4. i.e. REST API cannot add document to the column 2,3,4. Any solution or suggestion on this case? Thanks