Several previous posts have described what usually happens when your Indonesian passport expires and you haven’t formally renounced your Indonesian citizenship. For that reason I do not repeat this information.
It's important to remember that only the President of Indonesia has the authority to officially declare someone has lost their Indonesian citizenship, no one else. So unless you have formally renounced your Indonesian citizenship and approved by the president, it is still a grey area whether you have lost your Indonesian citizen.
As from the previous posts, In practice, it’s often not a problem to enter or leave Indonesia using a foreign passport, under these circumstances. I personally know a few people who have done so without issues. However, unless the person giving you advice is an immigration officer checking your passport at the border control, no one can guarantee 100% that you won’t face any problems. Rules can change, and unexpected situations can arise.
If you’re particularly worried and your foreign passport allow this, consider using the immigration E-gate to avoid direct interaction with immigration officers.