as others have already mentioned, there are several standards under development, while a handful of guidance documents were issued by various countries. UK is the most recent one I think.
There's are two from China, but they're in Chinese and I don't have a translated copy.
NMPA, “Technical Guideline on AI-Aided Software” (June 2019)
NMPA, “Introduction to review points for decision-making medical device software using deep learning technology” (September 2019).
In the US, in addition to the FDA's AI/ML action plan, there are two other relevant guidance documents from a few years ago. While their main focus are radiology devices, they are widely applied by the FDA reviewers to other device areas that use diagnostic software containing ML:
Computer-Assisted Detection Devices Applied to Radiology Images and Radiology Device Data - Premarket Notification [510(k)] Submissions
Clinical Performance Assessment: Considerations for Computer-Assisted Detection Devices Applied to Radiology Images and Radiology Device Data in - Premarket Notification (510(k)) Submissions