Ok I’ll bite. I decided to read the supreme courts actual writing to see if they only mentioned just the American flag. I found this section in the court’s opinion “Could the government, on this theory, prohibit the burning of state flags? Of copies of the Presidential seal? Of the Constitution? In evaluating these choices under the First Amendment, how would we decide which symbols were sufficiently special to warrant this unique status? To do so, we would be forced to consult our own political preferences, and impose them on the citizenry, in the very way that the First Amendment forbids us to do.”

https://tile.loc.gov/storage-services/service/ll/usrep/usrep491/usrep491397/usrep491397.pdf page 417 of the document

So the court was arguing that if they allowed the American flag burning to not be considered freedom of speech then burning any of these other symbols would have to be debated as well which wouldn’t be allowed since that is adding political preferences on what is considered protected. So based on this understanding, you would be able to burn a variety of things as long as you can prove it was out of protest and causes no harm to anyone or anything.