The travel eSIM installation guide is written for scanning a code on one phone. The same profile cannot be installed on a second device. These three devices are therefore not the same case.
A laptop or tablet with no cellular radio
It joins the hotspot the phone is already sharing. The hotspot shares the phone's data. It does not install the eSIM onto the computer. Steps, and what to check when it fails, are in hotspot troubleshooting.
A cellular iPad
A separate plan is possible only if that iPad itself supports eSIM. Check it the same way as a phone: Available eSIM in About, or an EID. If it supports eSIM, follow the installation guide on the iPad with its own plan. Do not scan the QR code already used on the phone. If it does not, use the phone hotspot. A rough model list is in compatibility. The check on your device is the one that counts.
A watch
The installation guide has no watch steps, and the product pages do not say a travel eSIM installs on a watch. The profile on the phone does not appear on the watch by itself. If the watch needs its own connection, ask the watch maker whether it can install a third-party eSIM. If it cannot, leave the watch paired to the phone.