The OP's image of the bellows compressed matches my own M605, I have 3 recessed lens boards, all similar in depth. No issues with any 50mm lenses, El Rokkor, Durst Neonon., Componon, Componon S. Comparon, Componar, El Nikkor, except the Rodenstock Trinar which came in a job lot, and I'd never even tried until today.
It is VERY CLEARLY not a Durst enlarger issue, rather a decision by Rodenstock to limit the Trinar/Rogonar 50mm f3.5 lens.
I would add that I had a 645 negative in my M605 enlarger and it was clear that wide open that the Triplet lens performance was rapidly deteriorating towards the edges & corners as expected.
It's a bit like using a Meyer Domiplan lens on a Pentax, Spotmatc you can't expect high quality results. Durst enlargers in the M600 series are high end enlargers, so why bother wasting paper with a low end budget lens.
Ian