Not a real replacement for AirDrop, since it still requires devices to be on the same network, instead of using ad-hoc Wi-Fi, but LocalSend is pretty nice.

Which features of Time Machine do you need? Just backing up, or do you also need the file history? For backups the best solution we have is probably Pika Backup (it uses Borg Backup under the hood, so it's compatible with other tools that use the same standard). There's a pretty good video about it: https://www.youtube.com/watch?v=W30wzKVwCHo
It also lets you grab individual files from a backup, but it doesn't look as nice as the Time Machine file history UI.