I cannot find any official document by SAP that states building a SAP Business One add-on using (both DI AND UI API) using .NET >= 5 is officially supported.
I've tryed building a .NET 7 test add-on and it seems to work. But I don't know if it is officially supported.
You can use any version of .NET, only problem would be when working with SAP B1 Forms. If you want to use visual studio template project then you will need to switch to .Net framework 4.8