doing a quick web search should bring lots of suggestions, but if anyone needed recommendations, all they had to do was ask nicely and preferably provide some information on what kind of machine and OS they’re using.
since i’m a Windows user, it would just use the Image Resizer in PowerToys. for Mac folks, it seems like Automator gives you way to resize batches of files.
since the original poster mentioned Photoshop, there’s also a way in that program to basically record set of actions that can be reapplied to a set of photos, and although i probably wouldn’t use that just for resizing (since Image Resizer and Automator are probably easier to use), it might be useful for a Photoshop user just to learn how to do this kind of thing so that they know how to automate other tasks.