You can open up %LocalAppData%\Google\AndroidStudio2024.3\log\idea.log (where 2024.3 should correspond with your GS version), search for "dl.google.com" and then find actual cause of your problem

To me, it's changed and faulty "Temp" folder (I changed it to ramdisk several years ago) and java simply can't r/w files on that ramdisk, thus making it display as "unavailable"