I cannot provide a fix for all, but in your position I would give reducing storage use to below 80% a try. We have had people here in this forum who also had just 5GB free and symptoms like unbearably slow responses from apps, too. Their FP2 often speeded up once they had freed up more space. If it works for you as well, keep it below 80%.
If you struggle to make so much “room”, I would recommend an SD card (formatted as “portable storage”! – warning: “extended internal storage” or whatever the other formatting is called has kept causing issues under Android 10) and move photos, videos and audio onto the card.