You left it a little too late.
Assuming that you were a British citizen at the time, had you moved, along with your family, to any other EEA member-state before 31st December 2020, you could have sponsored your mother to join you under EU law in that other EEA member-state.
If you were to move to another EEA member-state now, you would need to meet the same requirements as any other third country national and be subject to any limitations as them.
In
another thread on these forums, somebody had suggested looking at Canada and Australia as they have relatively liberal visas for parents of permanent residents and citizens. But in both those cases, you will be starting your immigration journey from scratch and it may be years before you can sponsor your parent on a long-term visa there.
You could of course look at moving to the country that your mother resides in, in South Asia, if the focus is on residing together.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.