Sorry to hear of your issues.
It's hard to comment as you haven't said what actually happened or why you think the claimed was denied. Normally they will give you a reason when writing to deny the claim @Julie-K-0
Personally for large claims like yours I wouldn't have tried to use the Airbnb Cover but claimed on my own home insurance for STR.
If you fully complied with how Airbnb asked you to submit information and your claim is for an area covered under their Cover, you can ask for independent arbitration and pay a fee which you will get back if you are successful or put in a claim with your STR insurance.