Python 3.9 has been released fairly recently and it was a bit too short notice for us to ensure it works with IDA 7.5 Service Pack 3 (if you have tried it, you may have had a bad time.)
We have now added support for Python 3.9 in IDAPython. Here’s how you can get it to work (only if you need Python 3.9; IDA already works fine with 3.8 or earlier versions):
Make sure you are using IDA 7.5 SP3
Download the appropriate package for your platform below
Unpack the package in the directory of your IDA installation
Run the idapyswitch binary (on Windows, from admin command prompt)
FleTime
