As someone who has a degree in "Computer Graphics and Mathematical Modelling" and worked as a CAD/CAM/CAE developer for over 17 years. I would say 100% you want a degree in computer science rather than mathematics if you want to pursue it as a career.
Mainly...
You need to know how to program, and beyond basic algorithms/problem solving. Actual hands on experience with a language used in industry. Doing a maths degree, you may go over some basics about program flow and algorithms etc, and you may do some basic programs in something like C (if you're lucky, although it may probably be something like matlab). But you will probably not go into certain concepts like OO, memory, compilers, optimisations, architecture etc, all of which are important in programming no matter which CS path you go down.
There are many concepts and processes you will need to understand and use in the industry (source control, issue tracking, tool chains) which you will not learn with a maths degree.
A computer science degree will no doubt be modular, and I highly suspect there will be modules specifically for computer graphics. This is very unlikely during a maths degree.
Modules in computer graphics will teach you many of the applicable fundamental concepts of computer graphics as well as exposing you to actual modern day graphics programming. There are many things we used to do in the fields of computer graphics which are just not done or needed these days (software rendering, rasterisers etc), but having the skill set you get from programming/CS degree, you will find it a lot easier to do these yourself to satisfy your own curiosity.
When you apply for your first job in industry, not having exposure to computing may put you at a disadvantage against other candidates who do (although having a maths a degree will have other advantages... see below).
While yes there is overlap, overall a mathematics degree will give you more theoretical skills but also give you more irrelevant knowledge in some quite complex fields of mathematics which will not ever be applicable in computing or specifically computer graphics.
A degree in mathematics is hard, harder than computer science, but it certainly says a lot about your capability to any future employer. It would carry a lot of prestige when looking for a career in computer graphics/software, and any interviewer/employer worth their salt would understand that you would probably be more than capable in the role with a maths degree. However, it also suggests limited exposure to fundamental concepts and processes in the software development world, and thus longer prep time to get you functioning efficiently. Problem solving and understanding concepts is just a part of professional software development, deadlines are a real thing and pressure is a real thing. You need a lot of discipline with processes, patience (bug hunting) and in many cases you need to find solutions which may not always be the most elegant or mathematically pure way of doing things, requiring you to be willing to make exceptions where required to get a solution.
Understanding strong mathematical conecepts is one thing, throw in things like floating point precision error and the fact that real-world data is never like the canned examples you get in scientific papers, and you soon realise that a deeper knowledge of programming with skill sets that are specific to programming (and nothing to do with maths) are required to actually implement this understanding into working solutions. These things you would learn with a CS degree rather than a maths degree.
I wouldn't have been able to do my first job without the degree I had as it gave me all the tools, skills and basic understanding I needed to do the job, but can honestly say I learnt more in the first 3 years of working in industry, and relevant experience, to doing the job that I do (and still love after all these years). I still learn today and suspect will keep learning for the rest of my career. In this respect, it's definately not impossible to have a very sucessful career in computer graphics without a CS degree (or more specifically a maths degree), and having a maths degree will keep more doors open for you, but ultimately, to get there faster, a CS background would be more advantageous.
Degree content may be very different these days (got my degree 20+ years ago), so I can only guide/suggest based on my academic experience. I would suggest also looking in to the modules that would be avaliable to you to fully understand what you would be doing, and then you can be better informed if they would be applicable to what you want to do.
For the record, my maths modules were (iirc)...
Calculus (many modules, higher dimension calculus, vector calculus etc), Geometry (Trigonometry), Groups and Set theory (Graphs, Cyclic groups etc), Trigonometry, Logic and flow, Statistics and Probability (Stochastic, dsitributions etc), Numerical analysis and methods (Newton, Monte Carlo, Fuzzy etc), Fluid Dynamics (losts of ODE, PDE, Fields etc), Number theory (Primes etc), Cryptography... plus others which I can't remember tbh...
And out of them, the areas of maths that I have used the most is geometry by far, with the rest taken up by numerical methods, fluid dynamics (I've done CFD work in the past) and more probability/statistics (tensors) these days...
Over my career, I always specialised more in the computer graphics and geometry realms, however this alone probably hasn't taken up half the time at work. Software architecture and other general stuff (bug fixing, not just in the realm of graphics, but anything) has also been a big part of my time at work.
I hope I haven't put you off with some of the things I have said. I can honestly say that software development (computer graphics) is a very rewarding career and feel priviledged that I made the career choice that I did all those years ago as I still love my job every day. The 'ups' far out-weigh the 'downs'.