I don’t know the details but both use services from the carrier. I think google hosts for the carriers but there are checks thats rely on the carrier. If you look at the details for google messages it address specific URLs based on the carrier.

For iPhone its all carrier depend. If the carrier doesn’t support it, iPhone will not have it.

Localsend is a good one to try out. Works with all devices and is pretty fast. It does however require an app to run.

For something you can run off the web on PC you can try pairdrop. This doesn’t require an app to work on PC. Haven’t tried it without the app on mobile so not sure if it will work on there via web.

I prefer Localsend over pairdrop due to local send being completely server less and all local.