Yeah GIMP is more than a decade behind Photoshop and a lot of other software in many respects.
It’s frustrating. Basic things like content-aware fill for small spaces, not even AI generating huge things for large missing pieces but removing some text over a person’s cheek or plaid shirt, something in total 100x100 pixels big or so. Just doesn’t exist. You can clone stuff but it’s not aware of things like the gradient of a shadow that it should match or a highlight or other basic things so you’re left doing extensive work using layers and then cleaning it up to be visually acceptable using multiple tools over 10 minutes of time whereas Photoshop does it with one tool in an instant.
There is AFAIK no way to do this.
Apple’s never open-sourced the APIs and interfaces and it only works on Macs and Windows. For this you will need to have either a Windows install (recommend separate drive so it doesn’t break Linux bootloader) or a persistent or not Windows VM with USB passthrough. I’m not even sure how well the VM situation works but it probably should. You don’t even have to have a license for Windows, you can just run it in the VM for this purpose alone but it does mean oh at least 40GB set aside on your drive for the VM image plus more if you want to do things like back-up the phone.