A: Yes. .NET 4.8 is backward-compatible with 4.7.2, 4.7, and 4.6. Your app will run without changes.
Ensure your server is fully updated via Windows Update. Install the latest Servicing Stack Update (SSU) and Cumulative Update (LCU) for Server 2016. Then retry the offline installer. .net framework 4.8 offline installer for windows server 2016