A fire simulation is not a mesh, it is a volume information holding certain data like density, temperature, flame etc.
So if you now bake a simulation (choose Format Volumes > OpenVDB under the domain's Cache settings) you can find different folders in the specified path, one is called "data". There all the fluid data is stored. One thing to note: if you want to keep the OpenVDB data file to import it to other blend files I would recommend to move or duplicate it (or the complete bake) in another location other than the designated cache path, otherwise you might accidentally free the bake in the domain and delete all files which you might have wanted to use later.
To import a single frame of these, you can use the Add menu in the 3D Viewport by pressing Shift+A and choose Volume > Import OpenVDB.
In the Import dialogue window navigate to the folder where the data is stored. The files are numbered, so if you want to import the data from e.g. frame 15, choose the file which is called "fluid_data_0015.vdb" and import it.
Now you have a volume object in the scene. If you go to the Object Data Properties tab you can see the data Grids stored in the file and which you can access in the material shader either through the Volume Info node or an Attribute node.
By the way, below the file name there is also a checkbox Sequence. If you enable it, you can enter the number of Frames, on which (scene) frame to Start the animation and the Offset is how many frames of the sequence you want to skip. Note that if you enable the sequence it does not matter if you opened file 0015 or 0001, it will always take the complete sequence into account and base frames, start and offset on that. This way you can import a full or partial fire simulation into a scene without the need to keep a domain, flow object etc.
Last but not least you can give this object a material like a Smoke Domain and render it as smoke and fire. The only I found is that somehow the same material looks different on a smoke domain than on a volume object. But with a little tweaking you can get basically the same look as with the simulation.