You can downgrade just filebeat, Elasticsearch and Kibana cannot be downgraded.
To downgrade it depend on how you installed, if you used rpm or deb, then you need to look on how to downgrade using the package mangement of your system.
I would recommend that you downgrade filebeat to 8.12.2, looking at the release notes for 8.13 there is a breaking change related to the netflow input.
- Convert netflow input to API v2 and disable event normalisation. 37901
Not sure exactly what was changed, but it is a breaking changing.
Also, 8.13.1 was released today, one week after 8.13.0, but there are no release notes for it yet.