ESP8266 Community Forum

https://github.com/esp8266/arduino-esp8266fs-plugin/issues/93
"Unfortunately there hasn't been a release since 2019, so it no longer works with the more recent versions of the Arduino IDE" .
You need to keep an older version of the IDE around if you wan to use this.

I have never used the IDE data upload as I prefer to build this functionality into the app which makes maintenance easier. This of course then works fine with IDE 2.0

You can see an example of this in the FSBrowser code under webserver or you can just use the simple file uploader included in that example.