As a chronic multitasker, I have been floored by the usability of Samsung's One UI on the Galaxy Fold 3 as well. It's a simple case of dragging and dropping apps where you want them, snapping into place with Windows 8-like intuitiveness. You can run up to three apps side by side on this thing, without any discernible degradation in performance. Although you may find that watching a YouTube video while streaming Xbox Game Pass alongside a web browser may chew through the battery if used with impunity, if I'm traveling for any particularly large length of time I'll most likely grab a power bank anyway. That's not to say the battery life is poor, though — it's anything but.
Samsung used new techniques to increase the brightness without impacting power consumption on its Fold 3 devices, and the difference is very noticeable compared to my Note 20 Ultra. I generally use this phone near to the lowest brightness setting while indoors, giving me anywhere up to 10 hours of non-stop screen time, albeit with 120Hz disabled. I found that an average day of use would net me anywhere up to 18+ hours on a single charge, which approaches Lumia 1520 power satisfaction.
Is the Galaxy Fold 3 for everybody, though? Probably not.