What is the difference between 'similar to' and 'similar as'?
We don't usually say 'similar as'. The word 'similar' is followed by 'to'.
For example 'Pepsi is similar to Coca Cola'.
The only situation in which you might come across 'similar' followed by 'as' is in a sentence like this:
'You should try to ensure that your two photos are as similar as possible'.
But in this sentence, the construction is 'as + adjective + as + possible', and you could put any adjective in the space. This is not a specific construction involving 'similar'.
In all other situations, you have to say 'similar to' + noun.