Here are some FOSS alternatives to Portal that don't depend on Chrome:
- ShareDrop (https://www.sharedrop.io): WebRTC-based P2P file transfers through the browser
- Sharik (https://github.com/marchellodev/sharik): File transfers via Wi-Fi or mobile hotspot for Android, iOS, Linux, and Windows
- KDE Connect (https://kdeconnect.kde.org): File transfers, notification sync, and other integrations between Android, Linux, Windows, and SailfishOS. Other compatible clients: Soduto for macOS (https://soduto.com), GSConnect for GNOME (https://extensions.gnome.org/extension/1319/gsconnect/)
- Syncthing (https://syncthing.net): Continuous P2P file syncing for Android, Linux, macOS, Windows, and BSD
- Wormhole (https://wormhole.app): File sharing from the browser through encrypted uploads that expire after a set amount of time or number of downloads