I think we need to distinguish between COM and OLE/ActiveX here. COM interop in .NET is two-way, and the consumer doesn't even need to be aware that there's a VM running the code that they're invoking. OLE is much more challenging, because the UI framework needs to be aware of it, and because it's built on Win32 UI primitives - so any framework that doesn't use those is going to have issues much like WPF (Qt is another example).
Bitness is not a new problem - VB6 similarly has problem consuming COM components written in C++, but compiled as 64-bit. Or, to put it another way: VB6 didn't have a problem, because 64-bit wasn't a thing back when it was popular, and didn't really became common on Win32 until relatively recently. But in a similar vein, if you always compile .NET code targeting x86 rather than AnyCPU (which is the default for new .NET VS projects - not sure when that changed, but it's been several years), you get the same exact behavior as VB6.
Getting back to OLE and ActiveX - I would say that it was killed by Microsoft directly, not because of .NET. Back in the day, most non-trivial Windows apps made by MS supported OLE for embedding - this was most commonly used with IE, but you could also do it with e.g. Word and Excel... until you couldn't anymore. If I remember correctly, it was Office 2007 that killed it as an officially supported scenario (you could still do it, but if anything broke, you were on your own). That roughly coincides with WPF, and I don't think that's a coincidence - but it doesn't mean that WPF/.NET was the primary cause.