A quick search at the Apple employment web site lists 600+ open jobs involved with software and hardware usability testing at quite a few of Apple’s offices in the US. Keep in mind that for every opening there are many more people currently in the same and similar positions.
I have been tangentially involved with UE, UI and eye tracking studies for product and online design and information architecture for websites, and worked with people who designed and managed them. But most of the 600 jobs consist of stuff I never even thought of even thought of, stuff like this. And this is just the in the US:
I looked at just three pages, and here are a very few openings I found particularly interesting. Health, Siri, AR, VR, voice, entertainment are heavily represented:
User Studies Exercise Physiologist
https://jobs.apple.com/en-us/details/200071471/user-studies-exercise-physiologist?team=HRDWR
Biomedical Studies Engineer
https://jobs.apple.com/en-us/details/200088492/biomedical-studies-engineer?team=HRDWR
Health Sensing Data Scientist
https://jobs.apple.com/en-us/details/200009616/health-sensing-data-scientist?team=HRDWR
Human Interface Design Senior User Studies Facilitator
https://jobs.apple.com/en-us/details/200054170/hid-senior-user-studies-facilitator?team=HRDWR
Software Engineer, Motion Algorithm Verification And Validation
Senior User Experience Designer, Create Machine Learning
https://jobs.apple.com/en-us/details/200022692/sr-user-experience-designer-create-ml?team=MLAI
Software Developer Engineer In Test
https://jobs.apple.com/en-us/details/200008390/software-developer-engineer-in-test?team=SFTWR
Technical Artist: AR Applications
https://jobs.apple.com/en-us/details/200000604/technical-artist-ar-applications?team=SFTWR
Senior QA Engineer, Augmented Reality Applications
https://jobs.apple.com/en-us/details/200000608/senior-qa-engineer-ar-applications?team=SFTWR
IOS Embedded Bring Up Engineer
https://jobs.apple.com/en-us/details/200057789/ios-embedded-bring-up-engineer?team=SFTWR
Siri Senior Software Engineer - Voice Experences And Domains
Siri Senior Program Manager: Siri Experience Team- Machine Learning and AI
https://jobs.apple.com/en-us/details/200027963/siri-program-manager-siri-experience?team=MLAI
Siri iOS Engineer
https://jobs.apple.com/en-us/details/200005013/siri-ios-engineer?team=MLAI
Senior Software Engineer, App Store
AI/ML iOS Mac Software Engineer
https://jobs.apple.com/en-us/details/200029696/ai-ml-ios-macos-software-engineer?team=MLAI
iOS Safari Software Engineer
https://jobs.apple.com/en-us/details/200071596/ios-safari-software-engineer?team=SFTWR
Years ago through work I did meet a few people who worked at Frog Design on the development of the original Mac as well as the Newton disaster. They said they did do usability testing and Steve Jobs was involved. They thought that the partnership with Apple ending was a combo of Apple wanting to bring industrial design in house and blame Newton on the dead guy. Steve was a hands on engineering, design and creative guy that greatly appreciated usability research, what he didn’t like was market research.