Given the completely different genre of films i'd be amazed if it was one of the actors. I assume he/she was an extra in both?
Quite, not really due to the genre but more location. AQOTWF was filmed mostly in Prague with a predominantly European (mainland) cast and a good chunk of BoD was shot in Yorkshire.
Possibly a walk-on or featured role in both. I'll have to ask them.
I personally don't think AQOTWF is that great an adaptation. Good film - poor adaptation. I can still appreciate both flips of the coin in this respect. If it wasn't an adaptation from a German classic then without a doubt it's a superb picture but it is and adaptation and I feel it failed in key parts to adapt in the right moments.
Interesting reading here in that regard - German critics haven't taken to it as well as the RoW critics have.
https://www.theguardian.com/film/2023/jan/27/oscar-all-quiet-on-the-western-front-germany-critics