I think itd be interesting to have fb lookalike app but its smf
Without specifics I'm not sure what you are after but you can start here; Mod about Facebook (https://custom.simplemachines.org/mods/index.php?action=search;basic_search=facebook).
Facebook UI was programmed by drunk monkeys. why would anyone ever want to recreate that?
The one person who made his site look like facebook also introduced HUGE numbers of issues
SMF is a forum and FB a Social Network. You can't create e social network with e forum script. They are two different worlds.
There were some Facebook like themes made before in the past.
Fb app's convenient. No need to scroll the screen left and right, fast to upload photo, comment, video.
The speed of content uploads are only as fast as the network's slowest device, or more commonly, the speed at which an ISP "graciously" lets you have, provided you pay up.
FB uses a trick on the front end to make it seem faster... dhtml/ajax.
Here's hoping that SMF 2.0 can become mobile friendly soon.
2.0 is as mobile friendly as its going to get.
development on 2.0.x is in maintenance mode which means fixing critical issues and applying security and other similar updates (like GDPR)
the 2.0.x default theme will not be receiving any updates.
There is the repsonsive-curve mod and at least a dozen responsive themes available for 2.0 which makes the forum mostly responsive.