It is not total crap. There is a ceiling limit of how much energy any human can expend. Even if you are a marathon runner, you will be capped at a certain level of expenditure per day and there comes a point where you cannot burn more calories even by exercising for longer, or you cannot get any more out of your muscles just by using them for longer.
Firstly and most importantly muscles need rest to be able to repair and grow, exercise is making small tears in them. So there is no point exhausting yourself doing 2-3 hours in a gym 7 days a week with no rest as it will not actually cause the muscles to grow any faster as they need to be rested and you could do 3 intense sessions a week at probably the same rate of growth with far far less risk of injury and over use.
try to remember OP is a beginner not someone who has already been working out for years. It is relevant in the context and not really very safe to advocate she spends 3 hours a day working out as she will injure herself.
science has showed that the "energy ceiling," which the scientists found to be common across all endurance activities they studied, is 2.5 times a human's rate of metabolism at rest, or roughly 4,000 kilocalories
Smart devices are really poor at calculating actual energy being used through exercise so they aren’t reliable. 4k calories burned would be the top level of a top athlete with good muscles that have spent years working at their physique.
Normal every day people (non athletes or long term gym goers ) are best to focus on food for weight and exercise for strength, mobility, toning, mental health and build up their endurance over time, not start with just exercising more and expect a weight loss result