2. How do I circumvent high fees?
Don't collect small Bitcoin inputs, use Segwit, and if possible use LN.
Using Bitcoin sidechain (such as Liquid or Rootstock) also works, but it's hard to find other people who use Bitcoin on any of those sidechain.
3. Why aren't developers tweaking the Bitcoin blockchain code to accommodate millions of transaction like Solana and BNB?
I don't know Solana but BNB is a centralized shitcoin made up by a rich guy. A centralized database can't be compared to a decentralized blockchain.
Solana also centralized and some people know Solana as coin that frequently going down.