Using Salesforce Apex and FileReader() and encodeURIComponent() from JavaScript, we can easily upload a file using Lightning Web Component lightning:input of type file.

Sample Code:

Apex Class:

public class FileUploadController {
    
    @AuraEnabled
    public static String uploadFile(
        String filename, String base64Content
    ) {
        ContentVersion objContentVersion = new ContentVersion();
        base64Content = EncodingUtil.urlDecode(
            base64Content, 
            'UTF-8'
        );
        objContentVersion.VersionData = EncodingUtil.base64Decode( 
            base64Content 
        );
        objContentVersion.Title = filename;
        objContentVersion.PathOnClient = filename;
        try {
            
            insert objContentVersion;
            
        } catch( DMLException e ) {
            
            System.debug(
                'Error while uploading the file ' +
                e.getMessage()
            );
            return e.getMessage();
            
        }        
        ContentDocumentLink objContentDocumentLink = new ContentDocumentLink();
        objContentDocumentLink.ContentDocumentId = [
            SELECT ContentDocumentId 
            FROM ContentVersion 
            WHERE Id =: objContentVersion.Id
        ].ContentDocumentId;
        objContentDocumentLink.ShareType = 'V';
        try {
            
            insert objContentDocumentLink;
            
        } catch( DMLException e ) {
            
            System.debug(
                'Error while uploading the file ' +
                e.getMessage()
            );
            return e.getMessage();
            
        }
        
        return 'File Uploaded Successfully';
        
    }
    
}

Lightning Web Component:

HTML:

<template>
	<lightning-card  title="File/Document/Attachment Upload">		
		<lightning-input 
			type="file"
			onchange={handleFileUpload}>
		</lightning-input>
		{fileName}
		<p slot="footer">
			<lightning-button 
				label="Upload"
				variant="brand"
				onclick={submitFile}>
			</lightning-button>
		</p>
	</lightning-card>
</template>

JavaScript:

import { LightningElement } from 'lwc';
import uploadFile from '@salesforce/apex/FileUploadController.uploadFile';
import { ShowToastEvent } from 'lightning/platformShowToastEvent';
export default class sampleLightningWebComponent extends LightningElement {

    fileName;
    fileInformation;

    handleFileUpload( event ) {

        let selectedFile = event.target.files[ 0 ];
        this.fileName = selectedFile.name;
        let reader = new FileReader();
        reader.onload = () => {
            let fileContent = reader.result.split( 
                ',' 
            )[ 1 ];
            this.fileInformation = {
                'fileName': selectedFile.name,
                'fileContent': fileContent
            }
        }
        reader.readAsDataURL( 
            selectedFile 
        );

    }

    submitFile() {

        let fileName = this.fileInformation.fileName;
        let fileContent = this.fileInformation.fileContent;
        console.log(
            'File Name is',
            fileName
        );

        uploadFile( { 
            filename: fileName, 
            base64Content: encodeURIComponent( 
                fileContent 
            )
        } ).then( result => {
            this.fileName = null;
            const toastEvent = new ShowToastEvent( {
                title: 'File Uploaded', 
                message: 'File Uploaded Successfully!!!', 
                variant:"success"
            } )
            this.dispatchEvent( toastEvent );
        } );

    }

}

js-meta.xml:

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>58.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__Tab</target>
    </targets>
</LightningComponentBundle>

Output: