Edit: Further edits as I missed the Nations League third place shootout!
All from Transfermarkt. I must confess and didn't realise until someone told me that TM's player data pages are weirdly missing a lot of high profile penalty shootouts, but they do include a random few. The exact numbers are therefore a little out. I strongly believe my main argument still stands though, which was that the cupboard was pretty bare after Kane and Rashford. I did quite a bit more manual research this morning and don't think anyone else has scored more than four penalties, in game or shootouts, for clubs at senior level, apart from Kane and Rashford. Sancho had scored 3/3 for Dortmund and one in the Nations League.
Maguire scored a couple for Leicester in shootouts and one in the Nations League, which made him a more obvious taker when you look further. But other than that? Grealish has scored one in a shootout for Villa but has only ever missed one during a game. Walker has scored one for Spurs in a shootout but right down at number nine or ten. Tripper has scored one for England but was unavailable, otherwise he would have likely taken one. Mount has another goal and another miss in shootouts for Chelsea. Sterling actually has scored in a shootout for City and England, but is 2-3 in matches. Phillips has scored one for Leeds. Shaw's penalty against Villareal was converted, but pretty crap way down the pecking order.
That still leaves you with Kane and Rashford as certainties. Maguire and Sancho the other players with at a couple of penalties taken and a 100% record at senior level. If Saka was performing well in training and you have faith in him, I can understand why. There's really not a good obvious candidate looking at all the data available.
The same manager's processes and approaches worked against Colombia and Switzerland. We shouldn't be too results-oriented after losing a single shootout.