The app would need to have a way to "escrow" the funds of everyone until everyone "signs" on the winer?

Only thing like this I've heard of is bitescrow.app, although I'm uncertain how many sigs can be added.

Your case is wading into the oracle problem, where there's no way to know who the winner of this golf competition is without a centralized authority, or a group of 3rd party API's, or a group of signatures. If you're a group of friends and family, it's probably easiest to do this by creating a free disposable LN wallet. Make it LNURL based with a cool name, everyone sends there, and the winner gets the invoice. Someone has to be designated the arbiter though. Doing it on L1 would be easy too, where you create a disposable wallet, give the xpub to everyone, everyone funds it, winner gets it, and everyone can literally see who claims it.

Yep, there are layer 2 solutions that can facilitate your wager with your friends without the need for everyone to download an app. One such solution is the Lightning Network, a second-layer protocol built on top of the Bitcoin blockchain. It enables fast and low-cost transactions.

For a progressive web app type of solution, you can explore custodial Lightning wallets like BlueWallet or Wallet of Satoshi. These wallets offer user-friendly interfaces accessible via web browsers, making it easier for your friends to participate in the wager without the hassle of app downloads.

With a Lightning wallet, you can create a shared payment channel with your friends, pool your wagers, and the winner can then collect their winnings efficiently and cost-effectively using the Lightning Network. Just ensure everyone involved is familiar with using Lightning wallets to avoid any confusion.