The black/silver stripe we can see at the left makes me think it might be a double-glazed unit, albeit a skinny one. The spread of visible damage from the cracks makes me think at least one surface is laminated.
You can order sealed unit double-glazing in any size, width by height by thickness, from any glazier. If these are anything like standard uPVC frames, the inside should have removable trim/retainers which are reasonably easy to remove. If it is a laminated pane, you would be best to take it to the glazier so they can match it with the new pane - or call them out. If you need to remove the trim to measure, you can just push a couple of them back in the meantime whilst you wait for the new pane to arrive.
Here's a particularly scruffy example from my workroom. The two trim pieces outlined in red just unclip - requires a little effort & two levers - and the entire glazed unit will then just lift out - they're not held in by adhesive or similar, just by the retaining trim. They clip back in afterwards.
Just to note that, contrary to several comments, you don't need to remove the frame to do this, just the trim.
Also, measurement is not vital to the absolute mm. These frames tend to have about 10-15mm overall play in the trim covering & you can shim underneath to bring the inside aluminium up to flush. Of course, you want to be as accurate as possible, not 15mm out, but don't go 'tight', leave a tad for expansion. Remove the trim before measuring so you can see how the installers measured it.