but is it safe to say my portfolio is lost if the developers don't restore the program
We can categorise wallets into two major types
A Custodial wallet is where some business controls the money in the wallet. they have the keys that control the money in the Bitcoin Blockchain, you don't. This is a bit like having an IOU instead of money. It is a bit like having an account at an unregulated bank rather than having cash in your pocket. The business is the custodian. If the custodian stops performing customers requests or goes out of business or stops responding to support messages, you have no recourse but to law. This is why it is important to research the business before giving it money.
A non-custodial wallet (sometimes called self-custodial) is where there is no custodian, no business who holds money. You control your money directly yourself. You run software on your own device that holds the private-keys on that device and which has very little or preferably no dependence on the developer's website or other services. This is the way Bitcoin was originally designed to work. No trusted third parties between you and the other party to a transaction. This is usually regarded as safer. In this case if the wallet developer is no longer available or if the wallet app stops working you can just transfer your private-keys to a different software wallet and carry on without losing any money.
So in conclusion, if the app is non-custodial, if app stops working your money is still safe (so long as you made backups of wallet and keys or recovery-phrase/seed-phrase). If the app is custodial, your money may be in peril.
The above answer is intended to be a general answer for all questions of a similar nature. However we can look at a specific instance.
Example: "Bitcoin Wallet" app by Coinbox Inc.
If the Youtube review is correct, your money has been stolen.