Mom thinks I’m wearing a mask

It’s so hard..& emotionally draining

Have you tried to recall pleasant times or an event you shared with your mom ? Photos?

my greatest fear is when my mom does not know me ..I have been her primary caregiver

Yup. I had to move my mother to SNF-MC because she started more and more to have this imposter syndrome, even thinking that I was a kidnapper. It became dangerous for us both, and others. (She once had an episode of this while I was driving at high speed on interstate, and thus tried to escape the car --> grab the steering wheel / gear shift --> knock me unconscious with her cane.)

Consider that in your mother's mind, you are likely a teenager or younger. So, your adult appearance does not match your mother's expectation of you. If you can be content to be your mother's "longtime friend" (try to alter your appearance if need be???), if she will accept that explanation, probably the best path forward. Resort to phone visits, if it gets dangerous for her/you/others.

My mother now has lost about the last 40 years of memory -- now stuck in ~1980. (I try to determine her timeline right away so that I know how to play along.) However, she can think that I am a teenager while at the same time knowing that she is 88 years old. It seem also sometimes thinking that I am a teenager while discussing my life as an adult. Competing/conflated facts. Dementia defying logic.