Docker build can't find Dockerfile even when it's the only file in the folder

user:/mnt/a/Projects/dir$ sudo docker build .
[+] Building 0.0s (2/2) FINISHED                                                                                                                                  docker:default
 => [internal] load build definition from Dockerfile                                                                                                                        0.0s
 => => transferring dockerfile: 2B                                                                                                                                          0.0s
 => [internal] load .dockerignore                                                                                                                                           0.0s
 => => transferring context: 2B                                                                                                                                             0.0s
ERROR: failed to solve: failed to read dockerfile: open /var/snap/docker/common/var-lib-docker/tmp/buildkit-mount3069745600/Dockerfile: no such file or directory
user:/mnt/a/Projects/dir$ ls
Dockerfile  node_modules  package.json  package-lock.json  public  README.md  src  vk-hosting-config.json
user:/mnt/a/Projects/dir$ cd Docker
user:/mnt/a/Projects/dir/Docker$ ls
Dockerfile
user:/mnt/a/Projects/dir/Docker$ sudo docker build .
[+] Building 0.1s (2/2) FINISHED                                                                                                                                  docker:default
 => [internal] load build definition from Dockerfile                                                                                                                        0.0s
 => => transferring dockerfile: 2B                                                                                                                                          0.0s
 => [internal] load .dockerignore                                                                                                                                           0.0s
 => => transferring context: 2B                                                                                                                                             0.0s
ERROR: failed to solve: failed to read dockerfile: open /var/snap/docker/common/var-lib-docker/tmp/buildkit-mount3184267428/Dockerfile: no such file or directory

All I see around on the web is advice on checking if the name is right, whether I’m in the right directory (done twice, including a directory where literally nothing besides the Dockerfile exists).

Providing /mnt/a/Projects/dir instead of . as context does nothing.

I’ve also tried various combinations for the -f flag (-f ./Dockerfile, -f Dockerfile in both the regular project folder and the Docker folder) — no dice.

Combining the last two options (full path to Dockerfile inside context, full path to context in one command) also didn’t help.

What do?