if statement with all combinations selectizeInput Shiny

I have a list of model tables based on all combinations of variables in a dataset. Depending on what variables are chosen in selectizeInput I want to return the associated model table in Shiny.

library(shiny)
library(flextable)
library(tidyverse)
vars <- names(iris)[-1]
vars_comb <- unlist(lapply(seq_along(vars), function(n) combn(vars, n, simplify = FALSE)), recursive = FALSE)
model_formula <- lapply(vars_comb, function(v) reformulate(v, "Sepal.Length"))
#create models
models <- lapply(model_formula, function(x) glm(x, data = iris))
names(models) <- model_formula
#create list of tables (flextable)
model_coeff_ft <- map(models, function(x) data.frame(x$coefficients) %>% 
                        rownames_to_column("Variables") %>% 
                     flextable() %>% 
                     set_caption("Table 1: Coefficients"))
#return table e.g.
model_coeff_ft[[15]] 


#shiny:
variable_names <- c("Sepal width" = "Sepal.Width", "Petal length" = "Petal.Length", "Petal width" = "Petal.Width", "Species" =  "Species")
ui <- fluidPage(
  titlePanel("Models"),
  sidebarLayout(
    sidebarPanel(
      selectizeInput("variables",
                     label = "Choose variable", choices = variable_names, multiple = TRUE, 
                     options = list(plugins = list('remove_button', 'drag_drop')))
    ),
    mainPanel(
      uiOutput("dataset_flextable")
    )
  )
)
#I NEED TO PUT IF STATEMENT IN HERE:
server <- function(input, output) {
  output$dataset_flextable <- renderUI({
    req(input$variables)
    get(input$variables) %>%
      htmltools_value()
  })
}
shinyApp(ui = ui, server = server)

so for example, when all variables are chosen:

I want to return:

but when only say, two variables are chosen:

I want the associated table returned:

etc...

I think i need to include an if statement in the server function but I'm unsure how to do this. I was thinking something along the lines of the following but I'm not sure how to make this more flexible to include all combinations and also unsure how to include it in the server side.

#vars
# [1] "Sepal.Width"  "Petal.Length" "Petal.Width"  "Species" 
#grepl or str_detect - if all variables selected then print model_coeff_ft[[15]]
if (all(str_detect(names(model_coeff_ft)[[15]], vars)) == TRUE) {
  model_coeff_ft[[15]]
}
#but i really need to reference all combinations somehow
names(model_coeff_ft)
# [1] "Sepal.Length ~ Sepal.Width"                                        "Sepal.Length ~ Petal.Length"                                      
#  [3] "Sepal.Length ~ Petal.Width"                                        "Sepal.Length ~ Species"                                           
#  [5] "Sepal.Length ~ Sepal.Width + Petal.Length"                         "Sepal.Length ~ Sepal.Width + Petal.Width"                         
#  [7] "Sepal.Length ~ Sepal.Width + Species"                              "Sepal.Length ~ Petal.Length + Petal.Width"                        
#  [9] "Sepal.Length ~ Petal.Length + Species"                             "Sepal.Length ~ Petal.Width + Species"                             
# [11] "Sepal.Length ~ Sepal.Width + Petal.Length + Petal.Width"           "Sepal.Length ~ Sepal.Width + Petal.Length + Species"              
# [13] "Sepal.Length ~ Sepal.Width + Petal.Width + Species"                "Sepal.Length ~ Petal.Length + Petal.Width + Species"              
# [15] "Sepal.Length ~ Sepal.Width + Petal.Length + Petal.Width + Species"

Any suggestions?

thanks