OpenVAS has a quality of detection (QoD) setting, which is used to filter out some of the less reliable tests. Each vulnerability test in OpenVAS is assigned a QoD score based on its reliability. Scanning with a QoD of 70% is a common default in the cybersecurity industry. To see all possible vulnerabilities you can lower the QoD setting all the way to 0% and scan again. At 0% you would expect to see more findings, but with more false positives.
You can change the QoD for your OpenVAS scan in the account settings page.
You can read more about OpenVAS QoD levels at https://docs.greenbone.net/GSM-Manual/gos-21.04/en/reports.html#quality-of-detection-concept and https://hostedscan.com/openvas-qod.