Just use private use area for your made-up-on-the-spot language. It's not a problem.

Do you have a symbols that satisfy the unicode consortium criteria? Submit a proposal.

Here is a good guide how to do is and be successfull: https://github.com/jloughry/Unicode/?tab=readme-ov-file#less...

Edit: I looked at some proposal for in Unicode 16. Some proposals are of poor quality (e.g. leafless tree emoji), some are good (numerals for Eastern Pwo Karen and Pa’O).