Mac mini 2023 suddenly not working with vga monitor - what's changed?!

We are a school and I bought a mac mini to test it would meet our requirements before buying more. Now I dare not go ahead because I intended them to run with our existing vga monitors and use an adapter. All worked fine but suddenly now that option doesn't work - monitor says no signal although if I plug the mac into a whiteboard there is visual. Has an update somehow made all my vga monitors redundant? I've tried every converter I have but nothing has worked. Very frustrating. Any thoughts?