Run lapply with lmer function on list of list

I am struggling with launching the lmer function on a data set comprising a list of lists. I have tried converting the list as a data frame too, but it returns an error

lapply(list, function(x) lapply(x, function(x) as.data.frame(x)))

lapply(list, function(x) lapply(x, function(x) 
      lmer(x[,4:7] ~ var + (1| id), x))) 

Error in model.frame.default(data = x, drop.unused.levels = TRUE, formula = x[, : not valid type (list) for the variable 'x'

Can anyone suggest something for running lmer through lapply?

reprex

library(tidyverse)
library(readxl)
require(writexl)
write_xlsx(mtcars, 'PQ_ele_com.xlsx')
        
dir = c('com', 'set', 'rit')
init = c('PQ', 'MG')
inpst = c('_ele_', '_mel_', '_col_')
           
for (i in dir) {
   for (j in init) {
      for (k in inpst){
        write_xlsx(mtcars, paste0(j, k, i, '.xlsx')) 
      }
   }
}
    
files = list.files(recursive= FALSE, full.names= FALSE)
     
init = c('PQ', 'MG')
dir = c('com', 'set', 'rit')
     
list3 = NULL
for (j in init){
   for (k in dir){
      df=c()
      for (i in files){
           if(str_detect(i, pattern = j) & str_detect(i, pattern = k)) {
             df=rbind(df,read_excel(i))}
         }
         list3[[j]][[k]] = df
      }
 }

Let's suppose I would like to fit lmer model through each sublists. For example:

lapply(list3, function(x) lapply(x, 
    function(x) lmer(x[,3:7]  ~ vs + (1| cyl), x))) 

It returns the error reported. Do you think it is possible to coerce it somehow?