I can indeed confirm that testing with a webserver using Bunkerized-Nginx as part of a suitable WebDAV server, that DAVx will get its requests blocked due to its user agent matching to ‘okhttp’.
As far as modding the filterlist itself, if the software using the filterlist allows passing a custom list location through, then it wouldn’t be hard to extract the line for ‘okhttp’ and remove it. The maintainer of the filterlist does not plan to change the list on its GitHub repo to remove ‘okhttp’.
For Bunkerized-Nginx specifically, the script that calls the filter list is static and calls the raw.githubusercontent page directly for sourcing it. Furthermore, no mechanism exists currently in the project to add exceptions to either of the two filterlists it pulls in for user agents. Making the primary option to fix the compatibility issue would be to disable user agent filtering entirely.
For circumventing the mechanism, the most consistent option would be to overwrite the resulting file /etc/nginx/user-agents.list inside of the running Docker/Podman instance of Bunkerized-Nginx, after the container has started and has finished its startup process. This circumvention will need to be done every time the container starts up, and it needs to wait until the container’s internal startup scripts finish before overwriting the file. This isn’t really a great solution as it requires to poke into a container regularly from the outside whilst it is running, as well as detection for Bunkerized-Nginx’s startup process needs to be monitored.
Another potential option would be to overwrite the script adding the filter list, though without the changes that need to be made being pushed to the github repo for Bunkerized-Nginx, they are likely to be overwritten any time the container updates, which may happen as much as every time an instance of the container is started. This is less favorable as it holds similar issues as the other circumvention as well as modifying the script should have more care put into it, as things may break when the source for the script updates.