Here is my Dockerfile:

...

FROM base AS runner

WORKDIR /app

RUN addgroup --system --gid 1001 nodejs
RUN adduser --system --uid 1001 nextjs

#
# Copy files
#

# Copy output:"standalone" traces (https://nextjs.org/docs/advanced-features/output-file-tracing)
COPY --from=builder --chown=nextjs:nodejs /app/public ./public
COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static

RUN ls -al
RUN ls -al node_modules

#
# Runtime definition
#

USER nextjs
ENV NEXT_TELEMETRY_DISABLED 1
ENV NODE_ENV production

CMD node server.js

then, when building, I can see sharp is listed into my node_modules:

$ docker build -t myapp .
...

#23 [runner 10/11] RUN ls -al
#23 0.116 total 40
#23 0.116 drwxr-xr-x    1 root     root          4096 Oct 25 07:32 .
#23 0.116 drwxr-xr-x    1 root     root          4096 Oct 25 07:32 ..
#23 0.116 -rw-r--r--    1 nextjs   nodejs        1828 Oct 25 07:32 .env
...
#24 0.122 drwxr-xr-x    4 nextjs   nodejs        4096 Oct 25 07:32 sharp
...

So why I get this error message when running the server:

Error: 'sharp' is required to be installed in standalone mode for the image optimization to function correctly. Read more at: https://nextjs.org/docs/messages/sharp-missing-in-production

$ docker run --rm -p 3000:3000 myapp
â–² Next.js 13.5.6
  - Local:        http://7d8a30f47cb2:3000
  - Network:      http://172.17.0.2:3000

 ✓ Ready in 73ms

Error: 'sharp' is required to be installed in standalone mode for the image optimization to function correctly. Read more at: https://nextjs.org/docs/messages/sharp-missing-in-production

Error: 'sharp' is required to be installed in standalone mode for the image optimization to function correctly. Read more at: https://nextjs.org/docs/messages/sharp-missing-in-production

...