I m just providing some thoughts from a perspective of an amateur, so just take my opinions with grains of salts. Personally, I do use both Photoshop and GIMP for basic image editing until now. Here are some key opinions.

1. Fundamentally, GIMP handle editing bit different from Photoshop. You can achieve most basic image editing with similar output quality for both software, ie. creating edited product images that used for product upload, creating banners, posters etc. But with GIMP, usually it take a lil more time to reach the same quality of output, like certain image format imported into GIMP and you need to add an alpha layer into it so that when you erase certain area, it will become transparent while not become background color. Whilst you can just straight forward do the erase with Photoshop without the need to do these manual steps. These kind of additional steps happened here and there within GIMP and cost more time.

2. If you solely do image edits and your workflow just stop there, surviving with GIMP is fine. But if your final works need to be shared / outputted for other usage, then Photoshop format is far more superior. For example, like I need to create an animated looping banner in MP4 format, a properly layered PSD file can be imported directly into Adobe After Effect while retaining their layers, then I could just manipulated each layer of them for desired effects, which is not something not achievable with GIMP.

3. Things will get trickier if the tasks got complicated like delighting & remove shadow, sharpen images, shadows and other filters. The way that blending and filters behave in GIMP are not exactly the same like Photoshop. One of the most obvious example is like drop shadow, in Photoshop, it can be toggle on and off easily on each layer but GIMP, the generated shadow will become part of the original layer or image and it is irreversible, you need a backup of original layer. So practice and experimenting is required for GIMP.

4. There is one thing that Photoshop that will never beat GIMP. IT IS FREE and available spontaneously as long as you have internet connection. There are a lot of occasions that I encounter the situations that I need to do quick edits at non-working environment without personal device. What I need is just a working PC at my client site or random guy's workstation, download GIMP, start edit, job done instantly without the need of searching for any device with photoshop. And, most of the time this impressed my employers, cause I got things done without asking specific tool and literally no software cost to the company.


Btw, there is something call Photopea, https://www.photopea.com/, that thing work like an online version of Photoshop. Hope that helps too.

tldr : if you want an career in this field, photoshop (able to use GIMP is a plus) ; for hobby and amateur job, GIMP, FREE