10cean Yes, GrapheneOS includes rollback protection, which prevents you from loading older firmware versions. However, you can manually install an older firmware version via a clean install, following these instructions (command-line installation guide).
However, keep in mind that a clean install will completely erase all data from your device. Be sure to back up all important data.
Immediately after booting your device for the first time after installation (even before connecting to the internet), you will need to disable automatic system updates. Otherwise, the first time you connect to the internet, GrapheneOS will attempt to update to the latest version, and you will be back to the original problem.
I also want to warn you that this will reduce your security. GrapheneOS regularly releases security updates, including fixes for critical vulnerabilities. Using an older version will expose you to known, publicly disclosed, and unpatched vulnerabilities. This makes your device much more vulnerable. It's also important to understand that weakening security directly undermines privacy, as vulnerabilities can be exploited to gain access to your personal data and bypass your privacy measures.