If there is an issue, chances are it's in the for-new-.NET implementation of WinForms. Any regressions in the GC or CoreLib themselves are definitely not expected and can be submitted as issues to be fixed.
There can be latency differences in edge cases of interaction between threadpool used by specific version and Overlapped IO on Windows, but that's likely about all there can be.
It's important to note that .NET Core 3.1 -> .NET 5 -> 6 -> 7 -> 8 is a huge difference in compiler and corelib internals (less so in GC, with major steps in 6, 7 and 8 in regards to regions and now DATAS), so an issue that could have existed in one of the previous versions is likely to be fixed by now.
There can be latency differences in edge cases of interaction between threadpool used by specific version and Overlapped IO on Windows, but that's likely about all there can be.
It's important to note that .NET Core 3.1 -> .NET 5 -> 6 -> 7 -> 8 is a huge difference in compiler and corelib internals (less so in GC, with major steps in 6, 7 and 8 in regards to regions and now DATAS), so an issue that could have existed in one of the previous versions is likely to be fixed by now.