Exemplo de conversão de base64 para blob e upload do blob

Upload Blob

UploadImagens(Conteudo) {
        return new Promise((resolve) => {
            fetch(Conteudo)
                .then(res => res.blob())
                .then(res => {

                    let fd = new FormData();
                    fd.append("blob", res, `${''.uuid()}.${Conteudo.substring("data:image/".length, Conteudo.indexOf(";base64"))}`);

                    fetch(this.upload, {
                        method: 'POST',
                        body: fd
                    })
                        .then(response => response.json())
                        .then(response => {
                            resolve(`${this.download}${response.name}`)
                        })
                        .catch(reason => {
                            console.debug(reason)
                        });
                })
        })
    }