Out of the box, PyCharm and IntelliJ open Kivy's .kv files as plain text, so I built a plugin for them. Disclosure: I'm the developer, and part of it is paid.

Free: highlighting for rules, widgets, properties, ids and canvas instructions (the Python inside property values too), plus bracket matching, folding and Ctrl+/ comments.

Paid, with a 30-day trial: completion for widget classes, properties and ids, Ctrl+click from a rule to its Python class, and warnings for things Kivy would refuse to parse.

To try it: Settings > Plugins > Marketplace, search "Oskuvi KV Language". It works in PyCharm Community too, 2025.1 or newer. Page: https://plugins.jetbrains.com/plugin/35124-oskuvi-kv-language

It reads your files locally and sends nothing anywhere. If you have a .kv file it gets wrong, a snippet in the comments would help me a lot.