I also thinking same but practically when I use safepal wallet (not recommended) there is dramatically a fee difference for different btc value. When I click on maximum btc(57$) ,the fee shows 11.86$ and with same network fee when I want to send 50$ then I have to pay 15$ fee.
What do you think it is wallet issues or something I have not learned yet?
It is not wallet issue, but the protocol. Bitcoin fees are calculated base on transaction size and that is why you see that even fee estimation platform put fee rate and not the exact fee to be paid because it varies. The number of input of output is what the fee rate is calculated against. For example the second transaction with $50 still has a change remain so the output will be the address you are sending the $50 to another address then the change goes to any of the change address making it 1 input and two output and that’s why there is difference in price to be paid.
This kind of cases is why it’s advisable to consolidate your little inputs into one when the fee rate is extremely low so that when you try to send you will have a single input and then would pay less than having multiple inputs