Fee estimation is very tricky for wallets. During times of network congestion the estimated fees can quickly grow beyond what's reasonable. It is possible to set your own total fee, but only if you know how large your transaction will be. (If you get to the pop-up where it asks you to confirm the transaction, it will give you the total fee it's going to use, and you can adjust your fee/kb from there). If you would like to decide for yourself what the best fee to get your transaction sent would be, you could use a site like
https://core.jochen-hoenicke.de/queue/#24h to use a fee appropriate for how long you want to wait for your transaction to be confirmed.
I believe the reason you cannot enter the total fee anymore, as opposed to the fee/byte is it's largely irrelevant compared to the fee/byte. Your transaction could contain many inputs, increasing it's size, but if you just send it with a "normal" fee, it's fee/byte ration will be much smaller and it will take much longer to confirm. This is provably a design decision to save users headache.
I also wouldn't use the bar, I would just type in the fee/kb myself if you were going to set a custom fee.