Hello,
I fixed it myself. Actually there are at least two solutions possible.

Solution #1. Replace it.

I saw a replacement lid on AliExpress, i.e. check this one

https://www.aliexpress.com/item/1005005293351017.html

but this does not guarantee that the replacement lid won't crack again. It sucks by design.

So my solution was #2 - please keep reading below

Solution #2. Fix-reinforce your cracked lid.
I bought

• this sheet of carbon - get the one which is 1mm thick (no need to get a thicker one, trust me). I think it is the cheapest carbon. It is good enough for our need. https://www.aliexpress.com/item/1005002317433412.html
• electronic repair tool kit https://www.amazon.ca/Precision-Screwdriver-RARTOP-Electronic-Portable/dp/B09ZNT56G1/ref%3Dsr_1_19?crid=GK94HUO21R91
• two component epoxy resin. Take the one which is not fast curing. At least 15 min cure time.
• C-clamp x4…6 pcs
• two pieces of rigid plastic or 5..7 mm plywood
• some fine grit sand paper. I do not remember which number, sorry. Just found it in my garage.
• 2-sided adhesive ribbon to attach your screen back to the lid. Watch some vids first then check Amazon, AliExpress, etc.

Open your laptop case, unscrew the screen, remove bezel. You need the lid to be free of everything else. There is a lot of vids on YouTube how to do it. Take your time, do not rush. It IS doable.

Cut the carbon sheet to match exactly the top surface of your lid. Remove the protective PVC film from one side only. Sand and smooth out the carbon edges, etc. Sand the surfaces to be glued: the carbon and the lid. The lid is made of aluminum. You don't need to sand it down to the metal, just remove the painting then you'll see the gray priming layer - no need to remove it. Also try to do not make a hole while sanding. It is just only a tiny bit thicker than beer can foil is. Cut the plywood (or plastic) to match the inner surface of your lid - the area where your LCD screen sits. You will need to squeeze the lid + glue + carbon sandwich in between the sheets of plywood using C-clamps. But it must not squeeze the framing edges of your lid. This is why the plywood must be able to get placed inside the lid. Prepare the epoxy resin, mix it up, apply very thin layer to both surfaces, to the lid and the carbon reinforcing sheet. Put them together. Check carefully the edges, remove the excess of epoxy. Finally, put the plywood to the top and bottom of your sandwich and clamp it together. Leave it to cure for some 24 hrs. Then you will need to re-assemble things back to enjoy your reinforced nice laptop.
I attach a couple of pics to give you better idea.
I think my result is well worth the effort. This laptop is good fast hardware in a badly engineered case. This is why I took time to fix it.
Good luck!

Hi,
it holds up well. No complaints. I was traveling a lot this year thus did open/close many times - no prob so far (…knocking on the wood… )) ) The glue is epoxy resin - like already said in my message above. It is important to get it glued properly.
To cut the carbon, I used a tool knife and a straight edge to draw a deep notch. After this slightly bend the carbon sheet and it breaks as drawn. Then put a sheet of sand paper over a perfect flat surface and smooth out the carbon edges. Be careful to do not breathe the carbon dust, put a mask on, etc or do it somewhere outside. You may find better way to cut carbon. I used whatever I had at hand.

the lid is not plastic, it's made of thin magnesium sheet then painted. This is why this laptop was the lightest available on the market.
The lid is still available through AliExpress at $75 CAD - use search. No need to buy it in Canada at x5..6 times more expensive. Then like I already said, the replacement lid probably won't last longer than the original one. So I think the best bet is to fix/reinforce the original one like I did.

Not only Acer uses magnesium. Check LG Gram - I bought one recently on a good discount for my girl who became university student this year. It has even bigger screen but feels somewhat sturdier.