[Service]
ExecStart=bash -c "nohup /opt/prometheus-2.53.0.linux-amd64/prometheus --config.file=/opt/prometheus-2.53.0.linux-amd64/prometheus.yml"&
Type=forking

this works

systemctl status prometheus --no-page
● prometheus.service - prometheus service
     Loaded: loaded (/etc/systemd/system/prometheus.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2024-08-28 13:04:28 CST; 1min 3s ago
    Process: 3280429 ExecStart=/usr/bin/bash -c nohup /opt/prometheus-2.53.0.linux-amd64/prometheus --config.file=/opt/prometheus-2.53.0.linux-amd64/prometheus.yml& (code=exited, status=0/SUCCESS)
   Main PID: 3280430 (prometheus)
      Tasks: 10 (limit: 19086)
     Memory: 42.7M
     CGroup: /system.slice/prometheus.service
             └─3280430 /opt/prometheus-2.53.0.linux-amd64/prometheus --config.file=/opt/prometheus-2.53.0.linux-amd64/prometheus.yml

timeout. because prometheus keeps in foreground.

Your service file asks systemd to wait for that. Remove the Type=forking and it will not.