Per this study, Intermittent Hypoxia-Hyperoxia Therapy (IHHT), also known as Contrast Oxygen, and one of the modalities at Gym for the Brain, improves functional capacity, health-related quality of life and objective and subjective symptomatic status of people suffering from Long COVID.
If you know someone with Long COVID, have them read the research, investigate Contrast Oxygen, and contact Gym for the Brain with questions.