Subsetting a font causes error on embedding.

[nnemes]

Hello I ahve a NodeJs environment, Typescript and using pdf-lib with '@pdf-lib/fontkit'.
I have a massive font to be able to support asian characters and I want to subset the font, so that only the used characters are included.

  private async createFontSubset(fontBytes: Buffer, annotationMap: Map<number, Annotation[]>): Promise<Uint8Array> {
    const font = fontkit.create(Uint8Array.from(fontBytes));
    const textArray = [];
    for (const annotations of annotationMap.values()) {
      for (const annotation of annotations) {
        textArray.push(annotation.text);
      }
    }
    const finalString = textArray.join('');
    const run = font.layout(finalString);
    const subset = font.createSubset();
    for (const glyph of run.glyphs) {
      subset.includeGlyph(glyph.id);
    }
    const subsetStream = await subset.encodeStream();
    const subsetFontData = await this.streamToUInt8Atrray(subsetStream);
    console.log('Subset font data: ', subsetFontData);
    return subsetFontData;
  }

  private async streamToUInt8Atrray(subsetStream: SubsetStream): Promise<Uint8Array> {
    return new Promise((resolve, reject) => {
      const chunks: Uint8Array[] = [];
      subsetStream.on('data', (chunk: Uint8Array) => {
        chunks.push(chunk);
      });
      subsetStream.on('end', () => {
        const totalLength = chunks.reduce((sum, chunk) => sum + chunk.length, 0);
        const combined = new Uint8Array(totalLength);
        let offset = 0;
        for (const chunk of chunks) {
          combined.set(chunk, offset);
          offset += chunk.length;
        }
        resolve(combined);
      });
    });
  }

However, when I do this

    const regularFontBytes = await fs.promises.readFile(regularFontPath);
    const subsetFontData = await this.createFontSubset(regularFontBytes, request.annotationMap);
    this.font = await outputPdf.embedFont(subsetFontData);

I get an error that

Error processing the request: Error: Unknown font format
    at Object.create (/Users/nnemes/Workspace/pdf-writer/node_modules/@pdf-lib/fontkit/dist/fontkit.umd.js:17842:12)
    at Function.<anonymous> (/Users/nnemes/Workspace/pdf-writer/node_modules/pdf-lib/cjs/core/embedders/CustomFontEmbedder.js:39:58)
    at step (/Users/nnemes/Workspace/pdf-writer/node_modules/tslib/tslib.js:141:27)
    at Object.next (/Users/nnemes/Workspace/pdf-writer/node_modules/tslib/tslib.js:122:57)
    at /Users/nnemes/Workspace/pdf-writer/node_modules/tslib/tslib.js:115:75
    at new Promise (<anonymous>)
    at Object.__awaiter (/Users/nnemes/Workspace/pdf-writer/node_modules/tslib/tslib.js:111:16)
    at CustomFontEmbedder.for (/Users/nnemes/Workspace/pdf-writer/node_modules/pdf-lib/cjs/core/embedders/CustomFontEmbedder.js:35:24)
    at PDFDocument.<anonymous> (/Users/nnemes/Workspace/pdf-writer/node_modules/pdf-lib/cjs/api/PDFDocument.js:883:79)
    at step (/Users/nnemes/Workspace/pdf-writer/node_modules/tslib/tslib.js:141:27)