It do!
(This is a minimal reproduction of emberjs/ember-cli-babel#419)
Clone and ember s; as soon as it hits tracked-built-ins, you'll see this output:
Build Error (broccoli-persistent-filter:Babel > [Babel: tracked-built-ins]) in tracked-built-ins/-private/object.js
/Users/ckrycho/dev/test/do-it-break/tracked-built-ins/-private/object.js: Class private methods are not enabled.
65 |
66 | // @private
> 67 | #readStorageFor(key) {
| ^
68 | let storage = this.#storages.get(key);
69 |
70 | if (storage === undefined) {
Stack Trace and Error Report: /var/folders/bw/k3jm2wf96p390m_k4jmhwm5c001321/T/error.dump.d6809848bc20bdeb895ea95b03bfbf87.log