The Excel specification states the maximum size of a column is 32k (32,767 characters). The Java action is behaving correctly. If you change the Java action, then Excel will probably throw an error when you try to use the data.
https://support.microsoft.com/en-us/office/excel-specifications-and-limits-1672b34d-7043-467e-8e27-269d656771c3#ID0EDBD=Newer_versions
If you need to store more data, you will need to pick another format such as CSV.
I hope this helps.