Lightroom isn't that good either. The watermarking dialog is very limited.
Should you need just basic text, there are a lot of free apps for that. For example, http://www.irfanview.com. Export your photos in TIFF or PNG format and then convert to JPEG with adding a watermark using IrfanView. I said to export in PNG or TIFF from Affinity because your photo will be resaved during watermarking. Every time you re-save a JPEG photo, a bit of quality is lost. So, it's better to export in a lossless format like PNG or TIFF, apply a watermark and only then save to JPEG.
Should you need more flexibility, use a more advanced app like https://www.visualwatermark.com or https://watermarkly.com. Both aren't free but they have a visual designer and can watermark photos in batches.
