The current version (3.1.1) and the upcoming version 3.2 don't support vulkan. Instead they support GLES2 and GLES3. (OpenGL)
Vulkan is being worked on and will be available in version 4.
But you can now start making games in Godot with GLES3 and be able to port your project over to version 4 and Vulkan when it is ready. (Maybe two step, first port to Version 4 and GLES3 and then switch to Vulkan)
The main developers said that they try to avoid breaking changes in Version 4 as much as possible. This means that you hopefully don't have THAT much work when switching from 3 to 4.
You can also use GLES2, especially if you want to support a wider range of hardware and keep requirements low. GLES2 will stay supported in Version 4.
Generally, renderers can be switched for a project but there are some caveats. For example you usually can switch most projects from GLES2 to GLES3. But GLES3 has some features which are not supported in GLES2 and won't work when you switch a project back from GLES3 to GLES2. An example are Particles. You'd have to use CPUParticles in GLES2 projects instead. CPUParticles also work in GLES3 but are less performant than "Particles".
Edit:
So basically Godot is just a Game Engine. And theoretically you wouldn't have to bother much about render Engines.
Practically, it won't hurt to think about your game requirements before you start.
What I'd say:
GLES2: Not THAT high fidelity
Wide (Casual) Audience (Notebooks, computers without separate graphics cards, slower CPUs)
or HTML5 (Browser) targeted
or (also) older mobile devices
GLES3: best graphics fidelity, most possibilities
Gamer Audience (Gaming Notebooks, PCs with - not too slow - graphics cards, newer MACs/Macbooks)
not all mobile devices (Some android devices fail with GLES3, many apple iOS devices will work with GLES3 for now)