What does the server currently do. If you are just serving files and have a smb share, those can be recreated under Scale easily. If you have Jails, plugins and a complex setup, we might make different suggestions.
Have you gone through the Core to Scale migration article or guide and done the checks? Geli encryption. No USB sticks for boot (recommendation) If you are stuck with USB, suggest a nvme or sata ssd in a USB adapter. USB sticks were wearing out quick. SMB sharing is done a bit differently and you don’t share a ROOT dataset, You create a Child dataset and share that.
The more details on your system, the more likely we might catch something.
Using an old NVIDIA graphics card? Latest drivers dropped support. Things like this.