Errors on "npm run dev" (after Laravel clean install) - laravel

Question

I'm very excited to learn Laravel and create a webapp based on a bootstrap template I bought (OneUI). I successfully installed Laravel (the /public route returns the default view to my browser correctly). Now i'm following the install guide of the template, and i'm experiencing problems with npm commands that return errors that I can't understand (I'm not familiar with npm).
I'd really appreciate if somebody could help me to find what's wrong so I could finally using Laravel with the Templates.
As requested in the OneUI documentation, i copy the public & resources folders, the routes/web.php file, and the webpack.mix.js file. Then, i install the npm dependencies running the following command :
npm i browser-sync browser-sync-webpack-plugin sass sass-loader bootstrap#^4.5.3 jquery#^3.5.1 jquery-scroll-lock#^3.1.3 jquery.appear#^1.0.1 js-cookie#^2.2.1 popper.js#^1.16.1 simplebar#^5.3.0 -D
This seems to run OK with a few warnings about some deprecated packages.
Then i run :
npm run dev
I get this return :
> # dev /volume1/web/dev/myproject
> npm run development
> # development /volume1/web/dev/myproject
> mix
events.js:287
throw er; // Unhandled 'error' event
^
Error: spawn npx ENOENT
at Process.ChildProcess._handle.onexit (internal/child_process.js:267:19)
at onErrorNT (internal/child_process.js:469:16)
at processTicksAndRejections (internal/process/task_queues.js:84:21)
Emitted 'error' event on ChildProcess instance at:
at Process.ChildProcess._handle.onexit (internal/child_process.js:273:12)
at onErrorNT (internal/child_process.js:469:16)
at processTicksAndRejections (internal/process/task_queues.js:84:21) {
errno: 'ENOENT',
code: 'ENOENT',
syscall: 'spawn npx',
path: 'npx',
spawnargs: [
'webpack',
'--progress',
'--config=node_modules/laravel-mix/setup/webpack.config.js'
]
}
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! # development: `mix`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the # development script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm ERR! A complete log of this run can be found in:
npm ERR! /var/services/homes/admin/.npm/_logs/2021-01-25T22_32_54_150Z-debug.log
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! # dev: `npm run development`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the # dev script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm ERR! A complete log of this run can be found in:
npm ERR! /var/services/homes/admin/.npm/_logs/2021-01-25T22_32_54_340Z-debug.log
This is on Linux, directly on my Synology (I don't use anything like a VM/Docker).
To install Laravel, I simply did this :
Installed php7.4 + libraries
Installed composer
Went into my web folder and entered the command : composer create-project laravel/laravel myproject
Added write access to my http user on the storage folder
I tryied this already without success :
As advised on other websites:
rm -rf node_modules
rm package-lock.json yarn.lock
npm cache clear --force
npm install
npm run dev
I tryied to do a npm install and npm run dev on a clean Laravel Install (before the install of all the packages required by the OneUI templates) to try to see if it's related to the OneUI files or the npm dependencies I installed. I have the same errors. So I understand it's not related to the OneUI install, but an issue with npm / my Laravel files (?).
In advance, thanks a lot for your help !