A major version is a good time for major innovation, including changes that are not backward-compatible.
Adoption of PHP8 is slow:
Some web hosting companies will cease supporting PHP 7.x as soon as PHP does. However, other hosting companies continue to offer it. Some charge extra for this service. They may want to incite clients to move to PHP 8.x which is better and uses fewer resources (hosting company saves on resources).
Even if PHP doesn't support PHP 7.4 anymore, some Linux distributions will backport security fixes. Check with your hosting provider for details.
The Tiki community has an automatic daily test upgrade from Tiki 24 to Tiki 25 with PHP 8.1 to monitor progress:
Please reach out to Marc Laporte if you can help. At this phase, we need developers that can help adapt code to PHP8 in Tiki, but also in external libraries that we get from Composer.
PHP8 brings massive innovations and will facilitate improving many things in Tiki, notably performance, error reporting and Realtime handling.
With such a big code base / feature set, it is a lot of work (and during some of the same period as the move from Bootstrap 4 to 5). If you have financial resources to sponsor the work, please reach out to Marc Laporte.