PHP 7.4 has been supported since I use it on my local development environment. As for archiving, it's still incomplete but feel free to contribute - there's a lot of design considerations to it that make it difficult to finalize. (It's a different approach than what NPFchan does)
Any code contribution to Tinyboard is highly appreciated, as it's an open source project supported completely by the community.
I see you haven't updated the repo since February, is the thing dead? or what are your plans?
I wouldn't call it dead. I intend to keep the code stable on recent releases of PHP until further notice.
I've just been really busy IRL, let alone lack motivation or manpower to add some of the bigger features.