Which instant exchanger is reliable for this ? could u suggest one ?
I've used FixedFloat for this, but only for small amounts. For privacy, using different exchangers is even better. BestChange has many options (but again: be careful who to trust).
what is the difference to cut it out the change from electrum with freezing or additional steps to avoid change balance like exchanging into lighting or Monero from an anonymity standpoint.
As far as I know, frozen inputs (or addresses) on Electrum are still communicated with the Electrum server when your wallet is running. Now that I think about it: the same happens to all addresses within Electrum's gap limit: both unused and used addresses are checked with Electrum's server.
is always safer to exchange bitcoin into another crypto for avoiding changing. ?
I'm not sure what you mean.
There are many ways to compromise your privacy, and many ways to avoid it. It really depends on your needs, and how much privacy you're looking for.