I just made to separate patch files (one for each function file) to help a bit further.  Most likely the patches need update before they are applied, I am pretty ignorant of how to do this properly. I assume this could be all included in a single patch file.

(file #55890, file #55891)

"pkg install financial" package for Octave 9.1 fails and returns error, as follows:

>> pkg install -local -forge financial

error: parse error near line 64 of file /Users/mattblake/.local/share/octave/api-v59/packages/financial-0.5.3/bolling.m

  syntax error

>>>     h = plot (x, asset, x, avg, x, avg .+ [-s, s], "-r");

                                                                 ^
error: called from
    doc_cache_create>create_cache at line 116 column 20
    gen_doc_cache_in_dir>@<anonymous> at line 150 column 20
    doc_cache_create>gen_doc_cache_in_dir at line 151 column 9
    doc_cache_create at line 62 column 12
    install>generate_lookfor_cache at line 836 column 5
    install at line 241 column 7
    pkg at line 619 column 9

>>

****
The error caret^ points up to the "+" sign.  Did I read that the ".+" operator no longer permitted?