Local lib-jitsi-meet

Hi,
I'm trying to create a react application that uses lib-jitsi-meet.
If I install the lib via npm I don't have problems, if I set up the package.json to use a local folder (I need to modify lib-jitsi-meet) I obtain the following error:

./node_modules/@jitsi/js-utils/jitsi-local-storage/index.js
SyntaxError: /Users/user/uncr/unicorn-app/app/node_modules/@jitsi/js-utils/jitsi-local-storage/index.js: Support for the experimental syntax 'classProperties' isn't currently enabled (11:14):

9 | * The object used for storage.
10 | /
11 | _storage = {};
| ^
12 |
13 | /*
14 | * Empties all keys out of the storage.

Add @babel/plugin-proposal-class-properties (https://git.io/vb4SL) to the 'plugins' section of your Babel config to enable transformation.

I tried to execute the eject and add @babel/plugin-proposal-class-properties and follow https://git.io/vb4S, but nothing.

do you have any advice about the solution?
Thanks
Angelo