A simple less-include triggers a deprecated-warning into the console - how to solve this issue?

[Neohiro79]

I don't know if I am just too stupid or the configuration system is buggy or a super secret special setting is unknown, but I got this error-message or "warning" in the console:

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file-manager.js:30 [Deprecation] Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/

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AFTER using a "shitty normal recommended "stylesheet.less" implementation like this one:

<link rel="stylesheet/less" type="text/css" href="myStyles.less" />

After studying your config-help for less, I assumed, I could just "disable" this warning in changing the logLevel from 1 into 0, but no - it won't work. So next thought, also changing the env-var into "production" - but no - it won't work.

While trying to find the reason for a "non-async-load-warning" while implementing a stupid "css" file (in this case it might be because of the "less" extension) I thought well, so just change the f* config-vars from "async: false" into "async: true" - but no, it won't work, so also changing the "fileAsync: false" into "fileAsync: true" - and well - no - it just changed from "one-console-warning-message" into a new, even more powerful "console-and-red-screen-warning-missing-file-message":

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FileError: 'file:///D:/myWholePathGoesInHere/myStyles.less' wasn't found (0)

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Weather the file, nor the filename, nor the position has changed - all what changed, was the "config-setting".
So next thought, I might need to implement the css file in a different way, like ie.

like this site here suggests: https://www.filamentgroup.com/lab/load-css-simpler/

but - you might guessed it: no - it won't work, instead, even more "console-messages" are popping up.

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So my question is this:
As nice and as powerful less.js is - which settings in the config can be really used right now - or is there a secret enable config first setting I missed to make it work as expected, or did I miss a special implementation of the special less-file - all of which seems to be NOT documented ANYWHERE - at least I couldn't locate any helpful sentence for that specific settings in the documentation.