ExpressJS How to render every njk template file if exist

I want to render any njk file with express+nunjucks Examples I found online contain only:

app.get('/', function (req, res) {
    res.render('index.njk');
});

But how to implement this? Thank you

const express = require('express');
const nunjucks = require('nunjucks');

/*
options and other code is here
*/

// index.njk, contacts.njk, ..., anything.njk
app.get('any *.njk file', function (req, res) {
    
    if('any *.njk file exists' == true) {
        res.render('any *.njk file');
    } else {
       console.log('error 404');
       res.render('404.njk');
    }
});

update:

What I have now is:

app.get(/^\/.+\.njk$/, function (req, res) {
    let file = req.url.replace(/\//, '');
    // if(fileExists == true)
    res.render(file);
});

Easiest way to get file from request:

app.get("/:templateName", function (req, res) {
    res.render(req.params.templateName);
});

You can do this with route parameters.

For example:

app.get("/:templateName", function (req, res) {
  // Check if the file exists, render it etc.
  console.log(req.params.templateName);
});