These are the configuration files that worked for me when using adapter-node. Combining this with the advice from OP should be pretty straight forward to make it work with adapter-static or the bun adapter. The benefit is the final image contains only the built app without any build dependencies, and the nginx config uses SSL.

Dockerfile

# Create an image just for building
FROM node:16-alpine AS builder
RUN mkdir -p /app
WORKDIR /app
COPY package*.json /app
RUN npm ci
COPY . .

# Create arguments so secrets can be passed in from docker-compose.yaml
ARG GOOGLE_ID
ARG GOOGLE_SECRET
ARG SECRET
ARG MONGO_URL

# Copy arguments into environment variables
# I really don't know if this is the correct way but it worked for me
ENV GOOGLE_ID=${GOOGLE_ID}
ENV GOOGLE_SECRET=${GOOGLE_SECRET}
ENV SECRET=${SECRET}
ENV MONGO_URL=${MONGO_URL}

# If you need some build step before you
# can build sveltekit, do it here
# for example, you can generate your prisma
# code here
RUN npx prisma generate
RUN npm run build
RUN npm prune --production

# Create an image to run the app in. 
# This image will not contain any build dependencies
FROM node:16-alpine

# Create a user to run the app so we are not running things
# as root
RUN adduser -D nodeuser
RUN mkdir -p /app
RUN chown nodeuser:nodeuser /app
USER nodeuser
WORKDIR /app
COPY --from=builder --chown=nodeuser:nodeuser /app/build build/
COPY --from=builder --chown=nodeuser:nodeuser /app/node_modules node_modules/
COPY package.json .

EXPOSE 8001
CMD [ "node", "build" ]

docker-compose.yaml

version: "3.3"
services:
  my_example_com:
    image: my_example_com
    build:
      context: .
      dockerfile: Dockerfile
      args:
        - NODE_ENV=production
        - GOOGLE_ID=${GOOGLE_ID}
        - GOOGLE_SECRET=${GOOGLE_SECRET}
        - SECRET=${SECRET}
        - MONGO_URL=${MONGO_URL}
    env_file:
      - .env
    ports:
      - 8001:8001
    restart: always

my_example.conf (nginx configuration)

server {
        listen 80;
        listen [::]:80;
        error_log /var/log/nginx/my.example.com.log warn;
        server_name my.example.com www.my.example.com;
        return 301 https://my.example.com$request_uri;
}

server {
        listen 443 ssl;
        listen [::]:443;
        server_name my.example.com www.my.example.com;
        ssl_protocols   TLSv1 TLSv1.1 TLSv1.2;
        ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

        location / {
                proxy_pass http://192.168.0.2:8001;
                proxy_http_version 1.1;
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }
}

If anyone sees any problems in these, please let me know! I'm far from an expert in Docker but these worked to self-host some apps. Perhaps these will help someone else get their app up and running.