Tap on "Method", it will change to "Static" and then you can select 1sat/b or bigger in increments, 1,2,5 10 and ....I'm not sure what's next 20 or 25, that's the maximum of customization for fees you can get with the mobile version.
...20,30,50,70,100,150,200,300
I think the Mempool methods is a little more dynamic as it changes basing on the size of the transactions in the mempool, and it also shows the possible position of each displayed fee rate of the transaction from the mempool tip.
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OP was talking about the mobile phone version of electrum. Not desktop.