Why not just Maxima, Reduce, or Cadabra2?

Author of Symbolica here! If these packages work well for you, then just use them :) I don't have a lot of experience with using these tools, but the last time I tried the user experience isn't so great, because of lack of LSP support (no typing, autocomplete etc). It could have improved in the mean time. I believe the tools are also more oriented to polynomial algebra and no so much for manipulating general expressions.