If you are using the new 64-bit Windows runtime, you should be aware that it breaks every single existing DLL. I wouldn’t recommend using it unless you are confident that every extension you use can be updated.
As for my extensions in particular, a quick search shows that I have dozens of ones that use DLLs, and many of them have not been migrated to GMS2 (instead relying on compatibility scripts), so it will take a while to update all of them.
If it is extremely urgent, you may attempt to compile extensions yourself using the source code that is either included with the extension (for paid extensions) or linked on the extension page (for free extensions), though code changes may be required for - argument and return types vary 32-bit to 64-bit for many system functions.