Facebook Reels sit between Instagram and TikTok
Meta runs Reels across both Facebook and Instagram, but Facebook's version accepts a wider range of source material — a lot of Facebook Reels are cross-posts, re-uploads or clips lifted from Pages, which means the quality you can download varies far more than on Instagram.
Typical output is a vertical MP4 around 1080x1920, though re-uploaded clips are often noticeably lower because they were already compressed before they arrived.