im not op, just crossposting from some other spots with permission from the ops but will give some info for people who want to make something similar

Agree glowing outline would be good here. A glowing outline is something thats relatively easy to do and good to add even if just to have for an accessibility setting people can toggle. Easily addable without changing sprites by attaching a shader onto the player and theres lots of tutorials out on doing so such as https://www.youtube.com/watch?v=UBujOvMRNl0

For adding lighting to the player, thats also feasible although maybe a bit harder than the outline shader due to needing to mess with normal maps. Something some people do is add a normal map for the outermost pixels only (edge lighting)

Its theoretically also possible by just lighting up the entire sprite without a normal map or the entire sprite normal mapped but tends to not look great and makes the sprite a bit more unreadable