Hello and welcome to Apple Support Communities, milnuts!
Make sure both your MacBook Air and Roku TV are on the same Wi-Fi connection. If you have a VPN, make sure it's disabled just in case it's interfering.
Additionally, test after after updating macOS to troubleshoot: Update macOS on Mac - Apple Support
- "Before continuing, it's a good idea to back up your Mac.
- From the Apple menu in the corner of your screen, choose System Preferences.
- Click Software Update in the System Preferences window. Can't find Software Update?
- Software Update now checks for new software.
- If Software Update finds new software, click Update Now or Upgrade Now to install. You might be asked to restart or enter an administrator password.
- If Software Update says that your Mac is up to date, then no new software is currently available for your Mac model."
If the issue persists, check out the steps from Roku below to further troubleshoot:
How to use AirPlay and HomeKit with your Roku® streaming device
- "On your Apple device, find the video, song, photo, or podcast you wish to share.
- Tap or click the AirPlay video icon in video apps, or the AirPlay audio icon in music and other audio apps.
- Note: With some apps, you may need to tap or click the Share icon before you will see the AirPlay icon.
- Select your Roku device from the AirPlay menu.
Once playback begins, you can pause, fast forward, and rewind from your iPhone, iPad, or Mac, or you can use your Roku remote. When you want to stop streaming with AirPlay, you can press Home on your Roku remote."
Let us know the results.
Have a great day!
