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The NavigationMixin solution should work as well, with minor modification. According to this blog post, rather than using NavigationMixin.Navigate with type argument standard__namedPage and ContentDocumentId, you should be using standard__webPage along with the file URL.

    previewFile(file){
        
        if(!this.usedInCommunity){
            
            this[NavigationMixin.Navigate]({
                type: 'standard__namedPage',
                attributes: {
                    pageName: 'filePreview'
                },
                state : {
                    selectedRecordId: file.ContentDocumentId
                }
            });
        } else if(this.usedInCommunity){
            
            this[NavigationMixin.Navigate]({
                type: 'standard__webPage',
                attributes: {
                    url: file.fileUrl
                }
            }, false );
        }
        
    }