[Pelham]

Of course the text doesn’t explicitly say that it was a Passover meal so there is room for dispute. A German Lutheran wrote a scholarly book arguing for it being a Passover meal:

https://www.amazon.com/Eucharistic-Words-Jesus-Joachim-Jeremias/dp/0334004144

[Campion]

Of course the text doesn’t explicitly say that it was a Passover meal

???

You know that after two days is the Passover, and the Son of Man will be delivered up to be crucified. -- Matthew 26:2

Now on the first day of the Feast of Unleavened Bread the disciples came to Jesus, saying to Him, “Where do You want us to prepare for You to eat the Passover?” And He said, “Go into the city to a certain man, and say to him, ‘The Teacher says, “My time is at hand; I will keep the Passover at your house with My disciples.”’” So the disciples did as Jesus had directed them; and they prepared the Passover. -- Matthew 26:17-19

Then, six days before the Passover, Jesus came to Bethany, where Lazarus was who had been dead, whom He had raised from the dead. -- John 12:1

There are many other examples. Beyond any question, the events commemorated at Easter occurred at Passover, and the Last Supper was a seder.