Maybe it's similar to the Android app. If so:
1. Open Google Maps
2. Tap my profile photo at top right
3. Pick "Your Timeline" from the menu
4. Tap the cloud icon in top navbar
5. Toggle the option to enable cloud backup
1. Open Google Maps
2. Tap my profile photo at top right
3. Pick "Your Timeline" from the menu
4. Tap the cloud icon in top navbar
5. Toggle the option to enable cloud backup
The cloud had a slash through it, I tapped it and enabled the setting.