.NET 5 is long out of support and I wouldn’t target that for anything. Starting next November, .NET 8.0 and 9.0 will be the only supported runtimes.
As inconvenient as this is, the problem was created when strong naming was removed, not now. After a while, this will no longer be a problem.
Nevertheless, since the issue was caused by MongoDB, MongoDB should provide proper complete and correct guidance. And that could be a repo that users can build the driver from.