How can I find out without my family finding out if I’m still my mother's beneficiary?

POA is for use while your Mom is living. You can ask family who is Mom's current POA but they have no obligation to answer you, and these documents are seldom filed anywhere.
As to after death, the will, you will find that out when your Mom died. Probate Court filing is necessary and a public document.
You say that you are next of kin. Is your Mom suffering from Dementia? Who is paying her bills for her. Her bank may let you know who the POA is and your doctor may let you know who is her assigned Health Care under her directive.
But basically, you really cannot access private info on someone (your Mom) very easily if others in the family who is involved in care giving don't wish to share information with you.
Best way forward is to befriend those caring for Mom, ask if there is anything you can contribute. You may then trip into the answers to the questions you have.

Mom having Dementia would make it so she really can't change any of her documents. A lawyer usually will talk to the person alone making sure they are not being coerced.

I think a person claiming POA needs to show people they are. Especially u as an only child. I think you have a right to know. If someone other than you has been assigned, then they make the decisions based on Moms wishes. They don't have to tell u anything about her finances or her health. A POA may know where the Will is but they don't need to know whats in it. POA stops at death and then the Executor takes over. Once Will is in Probate, its up to the Executor to contact all beneficiaries. There will be an accting, and if u don't agree with it you can contest it.

If there is no Will then an Administrator needs to be assigned by the Probate Office to handled the decease's estate. As decease's child this could be you. Probably u over a family member. Once you make sure bills are paid and other requirements, the State will determine who inherits. You being the only child would inherit.

Don't think u can contest a beneficiary. My GFs father had his pension and insurance left to his sister. Not to his living wife or his 2 children.

The only way to find out if ur beneficary to a policy is to call the company who issued it. But you may need to know the policy number. They may not give u any info because Mom is still alive. They may tell you are or not but they probably won't tell you who is beneficiary.

POA ends at the time of death. All of the information that you are seeking is private. I don’t see how you can find any of this out while your mom is living.
Ask an attorney to explain your state laws to you.
Best of luck to you.

If you are next of kin and only child, and there is no spouse and no appointed POA then almost certainly you will be contacted about a failing parent by the social services of a hospital where your relative is admitted. There is honestly no other way to make certain who is POA other than asking around of family members. As to being a beneficiary, we find out if we are listed as one upon the death of someone, when the executor of the estate notifies us, or when probate is filed. Meanwhile, just assume you are not, and live life as though you alone are responsible for yourself.