I updated timeFormat: 12, in config.js and ran pm2 restart mm and it shows online.
npm run config:check returns
[2026-04-09 10:00:53.379] [LOG] [utils] Loading config …
[2026-04-09 10:00:53.394] [INFO] [utils] Checking config file /home/pi/MagicMirror/config/config.js …
[2026-04-09 10:00:53.581] [INFO] [utils] Your configuration file doesn’t contain syntax errors :)
[2026-04-09 10:00:53.582] [INFO] [utils] Checking modules structure configuration …
[2026-04-09 10:00:53.742] [INFO] [utils] Your modules structure configuration doesn’t contain errors :)

But any changes I make to config.js are not taking place. What could be wrong?

Use --update-env to update environment variables
[PM2] Applying action restartProcessId on app [mm](ids: [ 0 ])
[PM2] mm ✓
┌────┬───────┬─────────────┬─────────┬─────────┬──────────┬────────┬──────┬───────────┬──────────┬──────────┬──────────┬──────────┐
│ id │ name │ namespace │ version │ mode │ pid │ uptime │ ↺ │ status │ cpu │ mem │ user │ watching │
├────┼───────┼─────────────┼─────────┼─────────┼──────────┼────────┼──────┼───────────┼──────────┼──────────┼──────────┼──────────┤
│ 0 │ mm │ default │ N/A │ fork │ 8787 │ 0s │ 105 │ online │ 0% │ 2.6mb │ pi │ disabled │