No. You do not necessarily need a return ticket back to your home country.
However, when entering the UK with a UK ETA, you may need to show that you plan to leave the UK after your visit. This means that an onward ticket to another country or a clear travel itinerary may also be helpful, even if it is not a return ticket to your home country.
The important point is whether your plan to leave the UK after your visit can be confirmed, not whether the ticket is specifically a round-trip ticket.
If you only have a one-way ticket, you may be asked additional questions during entry checks. Therefore, it is recommended to prepare an onward ticket, travel itinerary, accommodation details, or other supporting information if available.