This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 靻 is uncertain. It combines 革 (leather) with 且, but the role of 且 is unclear.
With 革 (leather) on the left and 且 on the right, 靻 might suggest something made of leather, but its meaning is unclear.
For ソ, imagine sewing a piece of leather: sew -> ソ, and the leather component 革 hints at the material.