SS has access to your Medicare records. So, you're disclosing the info or not won't make a difference.

The cost of your treatment, including Baker Act hospitalizations, won't be a factor in your continuing to receive SSI/SSDI benefits. Is there any advantage in terms of SS benefits to being hospitalized? No, not IMO. But nor is there any harm, UNLESS it's a sign that you're not adequately attempting to address your mental health issues. Ideally, you should be seeing a mental health provider weekly, and you must take your meds as prescribed.

If you choose to work and make over 50% of SGA a month, expect to receive the Long Form CDR.

No, the form won't ask about the Baker Act specifically. But question 6 of the Short Form (SSA-455-OCR-SM) asks about hospitalizations.

I have never heard or read of anyone being cut from Medicare because their illness and/or disability cost them too much! Medicare does not follow the same rules as health insurance companies because it is a FEDERAL program. Health insurance companies are governed by the "State."