I don’t think a week is that long to wait for an open source project like this. I suspect as soon as they released 115 they got a deluge of bug reports that are probably keeping them occupied.
Granted, I’m not personally affected because <smug>I use Arch btw</smug>. But on a serious note, it makes sense to me that “bleeding edge” distros where users expect the latest versions quickly would package Thunderbird for their repos, whereas those on more stability-focused distros would wait the couple of weeks for the Flatpak.