I've seen on Telegram during last weeks around 3 old (like 10y old with no activity) wallets selling their btc.
Telegram, scammer's paradise and wallets for sale are almost certainly 100% a scam, especially if they pretend to contain many years old coins in eye-watering quantities. Be careful with strangers on Telegram!
What are the chances that these wallets are actually broken by bruteforce? I know there were discussions some years ago about people that were trying to crack the private keys.
Probably 0% because the scammers earn money by selling such forged wallets and don't want their victims to discover that those wallets don't contain the required private keys to move the funds. So there's clearly no interest in anyone being able to actually break the wallet's encryption password.
What do you think guys? Can such successful act would mean the end of btc era?
What do you mean? Why would something basically impossible be the end of Bitcoin era?
I have a feeling you don't understand the security of Bitcoin at all. Educate yourself!
Besides a few known transactions by Satoshi Nakamoto, none of his mined coins have been moved/stolen by someone else. And Satoshi used P2PK coinbase transactions, ie. the public key is known on the blockchain. His coins are still secure, so are yours, so are mine (with respect to the basic technical security implemented in Bitcoin).
If you do stupid things with your wallet and ignore computer security, you can loose your coins, but this is not Bitcoin's fault.