… access datasests inependent on its upper or lower case?

If you only now the string but not whether it is writen upper lower case or anything inbetween use this line:

import h5rdmtoolbox as h5tbx
h5tbx.use(None)

with h5tbx.File() as h5:
    h5.create_dataset('TEST', data=1)
    print(h5[h5tbx.lower('test')])

<HDF5 dataset "TEST": shape (), type "<i8", convention "h5py">