Asd,
In motorracing, any bit of weight that does not contribute to the car going faster, is either a waste, an oversight, for safety reasons or there because of the rulebook only, but then put to good use as moveable ballast.
The higher up the ladder, the more rigorous this 'rule' applies. (Or maybe I should say 'used to apply', as the FiA has been messing it up pretty decently over the last years.)
It's the first thing you start looking for to make a car -any car- faster and more nimble. So if it's possible to shed weight, that's what you do - normally.
But then they also race pickups in the states, which, to my opinion, borders insanity, even if anything unnecessary has been taken out. What's next, racing Caterpillar Shovels?
Owning a sports-/racingcar that's 40% lighter than the current generation F1 cars makes you see the light.

Try portuguese.

We have new rules generally means there's old rules too. We have a new engine generally etc.
That's not a 'take on english', it's normal interpretation.

First sentence:

IndyCar has further delayed the introduction of its new hybrid power units, which were due to appear for the first time in the opening race of the 2024 season.

And without ambiguity:

IndyCar has further delayed the introduction of hybrid power units, which were etc.

Just ditch the 'its new' and you're there; no confusion, as 'Introduction of' already means it wasn't there before.

"But then it is in contrast with (other) news saying they have successfully shed weight chassis wise. Another matter, but if that’s possible, then why on earth wasn’t that done earlier?"
- That's not a sensible question. Let's take the aero screen, where they plan to shed 5-7kgs from:
It took them a lot of time, money and resources (which even involved an aviation company) to create the aero screen. And the aero screen was perfectly fine. There was no need to re-do it every year only because it was possible.
Now, a valid reason to further develop the aero-screen (and make it lighter) has occured, so they again invested time, money and resources for that purpose.
There was no reason or sense to do it earlier. The same goes for the chassis.

.. the introduction of its new hybrid power units ..

suggests there are old hybrid power units too, but there aren’t.

Interesting interpretation. Been awhile since grammar classes, but I'm pretty sure that the hybrid power units are new. That doesn't necessarily mean there are hybrid power units that are old- that might be phrased as "replacement hybrid power units". An F1 driver might have a "new power unit" in their car, but if it's the first race of the season, that doesn't mean it replaced an old unit.

I can see why English drives non-native English speakers crazy.

As an American who watches European politics with some amusement, I find your poorly worded expression of denigration more exasperating than informative- if anti-hybrid sentiment were that strong, the engine wouldn't be introduced at all.

I would expect they've found a technical issue that needs a bit more time to iron out.

IndyCar's hybrid system utilizes super capacitor technology to store electrical energy, so the weight gain and size is much less than F1's hybrid system. Most series use batteries to store energy, but the super capacitor helps to keep the weight down and the amount of space taken up to a minimum. A motor generator unit (MGU) is fitted at the rear where the remote starter currently used attaches to the gearbox, while the super capacitor is inside the gearbox casing. Packaging is quite a challenge. It should give about a 150 HP boost when utilized, over the current 50 HP for push to pass.

.. the introduction of its new hybrid power units ..

suggests there are old hybrid power units too, but there aren't.

Their current engine is a 2.2 ltr twin turbo V6, so ice only. That's been around since 2012 already, which gives me mixed feelings. Indy does not seem to have lost much of it's fanbase, despite running that same engine for what can be considered as 'ages', in motorsport terms. I must confess though, that I'm no Indy insider, and there may well be people -like me, where F1 is concerned- that would love to see more development being allowed and brought. On the other hand, going hybrid makes things complicated, expensive and heavy, non of which I'm particularly a fan of, to say the least. Initially, they were supposed to go to 2.4 ltr hybrids, but that was already abandoned, with them sticking to 2.2 ltr.

Given what they tell us, there is only one explanation for them to postpone the introduction of hybrids, and that is that they're not quite happy with where the -jointly Chevrolet and Honda- development stands, at the time of the decision. Whether it's about overall weight, the weight distribution, dimensions, reliability or power output? Would be nice to know. But it is the Divides States of America; maybe there's anti-hybrid sentiments at work?

If they do indeed switch to the new engines during the season, does that mean they switch to new chassis as well? Seems like a very weird decision to do all that mid season, even if the article suggests they switch to the new engines only. But that means the swap is supposed to be rather seemless in terms of weight and weight distribution, meaning car handling, as well as where the 'bolts and nuts' go. But then it is in contrast with (other) news saying they have successfully shed weight chassis wise. Another matter, but if that's possible, then why on earth wasn't that done earlier?

All in all, this brings me more questions than answers.