Hi J,
Thanks for contacting Syncfusion.
We want to let you know that we have provided support for .NET 5.0 RC from our v18.3.0.35 releases. However, we are working on providing support for .NET 5.0 for both Server and WASM and it will be available from our Volume 4 2020 release which will be scheduled for the end of December 2020.
And, we suspect that you have directly overwritten the target framework as 3.1 in the .NET 5.0 WASM application. So that your application is not running anymore. In 3.1 based WASM application has netstandard2.1 as the target framework. Please refer to the below comparison for .NET5.0 and .NET Core 3.1 based webAssembly application.
| .NET 5.0 WebAssembly |
.NET Core 3.1 WebAssembly |

|

|
Kindly please make the above changes or Create the new wasm application in 3.1.
Please let us know if we have misunderstood your query and any concerns on this.
Regards,
Muthukumar K