Reactive Dataframe in Rshiny

I have a data frame which consist of multiple categories and month. Each row is 1 interaction by the participant so I want to show by the month and the different categories their interaction count throughout the year through a heatmap. A total of 4.9 million rows which means there is a total of 4.9million interactions throughout the year.

I tried to use an input to indicate the column name and tried to reactively change the X axis but it does not seem to work.

library(shiny)
library (igraph)
library (tidygraph)
library (ggraph)
library (plotly)

interaction <- readRDS("participant_interaction.rds")

# Define UI for application that draws a histogram
ui <- fluidPage(

    # Application title
    titlePanel("Social Network Interaction"),

    # Sidebar with a slider input for number of bins 
    sidebarLayout(
        sidebarPanel(
          helpText(" Visualise the Social Network Interaction of the Population
          in Ohio"),
          
            selectInput(inputId = "Category",
                        label = "Choose a Category",
                        choices = c( "Household Size" = "Household_Size",
                                     "Have Kids" = "Have_Kids",
                                     "Education Level" = "Education_Level",
                                     "Interest Group" = "Interest_Group",
                                     "Age Group" = "Age_Group"
                        ),
                        selected = "Household_Size")
        ),

        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("heatmapPlot")
        )
    )
)


server <- function(input, output, session) {
  
  dataset <- reactive({
    interaction %>%
      group_by(Month,input$Category)%>%
      summarise(InteractionCount = n()) %>%
      ungroup
  })

    output$heatmapPlot <- renderPlot({
      ggplot(dataset(),aes(x= input$Category,y = Month,fill = InteractionCount)) +
        geom_tile()
    })
}

# Run the application 
shinyApp(ui = ui, server = server)

Desired Output:

Current Output:

my random 20 (dput) for my RDS file:

structure(list(Participant_ID = c(374, 167, 899, 299, 443, 889, 
997, 521, 953, 436, 218, 422, 4, 227, 126, 12, 57, 386, 255, 
307), Month = structure(c(7L, 8L, 9L, 9L, 6L, 10L, 11L, 7L, 4L, 
6L, 10L, 11L, 8L, 12L, 7L, 8L, 7L, 11L, 7L, 10L), .Label = c("Jan", 
"Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", 
"Nov", "Dec"), class = c("ordered", "factor")), Income = c(37891.66, 
50156.67, 59877.49, 56393.02, 27899.58, 61258.05, 60728.21, 44858.08, 
36665.14, 27970.52, 27803.1, 63058.55, 135076.17, 46147.7, 30712.52, 
93774.11, 168620.22, 82925.21, 29451.88, 40328.79), Expenses = c(-26931.38, 
-32313.29, -25363.68, -23341.46, -24747.06, -18336.36, -17067.74, 
-22054.58, -23258.78, -22504.3, -23833.48, -17322.96, -28322.98, 
-16633.05, -23661.04, -21135.57, -20642.13, -23707.51, -26028.96, 
-30125.43), Household_Size = c(2, 2, 2, 3, 1, 2, 1, 3, 1, 1, 
1, 1, 3, 1, 2, 3, 3, 2, 3, 3), Have_Kids = c(FALSE, FALSE, FALSE, 
TRUE, FALSE, FALSE, FALSE, TRUE, FALSE, FALSE, FALSE, FALSE, 
TRUE, FALSE, FALSE, TRUE, TRUE, FALSE, TRUE, TRUE), Age = c(57, 
49, 59, 35, 56, 19, 48, 39, 45, 36, 38, 27, 43, 59, 26, 34, 56, 
39, 59, 38), Education_Level = c("High School or College", "High School or College", 
"Graduate", "High School or College", "High School or College", 
"Bachelors", "Graduate", "High School or College", "Graduate", 
"High School or College", "High School or College", "Graduate", 
"Bachelors", "High School or College", "High School or College", 
"High School or College", "Graduate", "Graduate", "High School or College", 
"Graduate"), Interest_Group = c("F", "F", "B", "I", "F", "A", 
"I", "I", "G", "J", "B", "D", "H", "H", "A", "D", "A", "H", "H", 
"H"), Joviality = c(0.85417223, 0.846680285, 0.544405537, 0.5149016, 
0.758121962, 0.126644557, 0.128853966, 0.477456741, 0.846871205, 
0.949412047, 0.971074532, 0.647441392, 0.857396691, 0.490213553, 
0.72895287, 0.241615182, 0.422849796, 0.479804894, 0.852187763, 
0.962210067), Age_Group = structure(c(9L, 7L, 9L, 4L, 9L, 1L, 
7L, 5L, 6L, 5L, 5L, 3L, 6L, 9L, 3L, 4L, 9L, 5L, 9L, 5L), .Label = c("20 & Below", 
"21-25", "26-30", "31-35", "36-40", "41-45", "46-50", "51-55", 
"56-60"), class = "factor")), row.names = c(1970773L, 932225L, 
4348108L, 1549925L, 2381951L, 4296595L, 4822673L, 2808545L, 4594431L, 
2337980L, 1146486L, 2241290L, 16905L, 1187579L, 697338L, 71056L, 
302316L, 2012670L, 1319716L, 1594018L), class = "data.frame")