op here. After hours trying different curl built in versions, a work colleague came with the idea of manually installing the curl version of our choice (I knew from personal installation that 8.4.0 had both GSS-API and SPNEGO features enabled) inside the container this way:

RUN wget https://curl.se/download/curl-8.4.0.tar.gz && \
tar -xzf curl-8.4.0.tar.gz && \
cd curl-8.4.0 && \
./configure --with-gssapi --with-ssl && \
make && make install

Note: needed dependencies were installed too so that could work, making the image slightly heavier than it should for what's required, please reach out in case you need troubleshooting with something similar, as not having every dependency will trigger a failure during the make install and configuration steps