OpenGL is fine, it has the same issues now it had before but none of it really comes from "old age" or being deprecated in any way. It's not as debuggable and much harder to get good performance out of than the lower level APIs but beyond that it's still great.

Honestly, starting out with OpenGL and moving to DX12 (which gets translated to Vulkan on Linux very reliably) is not a bad plan overall; DX12 is IMO a nicer and better API than Vulkan while still retaining the qualities that makes it an appropriate one once you actually want control.

Edit:

I would like to say that I really think one ought to use DSA (Direct State Access) and generally as modern of a OpenGL usage as one can, though. It's easy to get bamboozled into using older APIs because a lot of tutorials will do so, but you need to translate those things into modern modern OpenGL instead; trust me, it's worth it.

Actual modern OpenGL is not as overtly about global state as the older API so at the very least you're removing large clusters of bugs by using DSA.

What do you think makes DX12 better API than Vulkan?

I've found it has less idiosyncrasies, is slightly less tedious in general and provides a lot of the same control, so I don't really see much of an upside to using Vulkan. I don't love the stupid OO-ness of DX12 but I haven't found it to have much of an adverse effect on performance so I've just accepted it.

On top of that you can just use a much better shading language (HLSL) with DX12 by default without jumping through hoops. I did set up HLSL usage in Vulkan as well but I'm not in love with the idea of having to add decorators everywhere and using a 2nd class citizen (sort of) language to do things. The mapping from HLSL to Vulkan was also good enough but still just a mapping; it didn't always feel super straight forward.

(Edit: To spell it out properly, I initially used GLSL because I'm used to it from OpenGL and had previously written some Vulkan shaders, but the reason I didn't end up using GLSL is because it's just very, very bad in comparison to HLSL. I would maybe use some other language if everything else didn't seem so overwrought.)

I don't hate Vulkan, mind you, I just wouldn't recommend it over DX12 and I certainly just prefer using DX12. In the interest of having less translation going on for future applications/games I might switch to Vulkan, though, but still just write for Win32.

OpenGL is still be the best for compatibility in my opinion. I have been able to get my software using OpenGL to run on Linux, Windows, old/new phones, Intel integrated graphics and Nvidia. Unless you have very specific requirements it does everything you need and with a little care, plenty fast.