Please be advised: currently, the only travel bubble Taiwan has is between Taiwan & Palaw.

Singapore indeed is among the next in line travel bubbles Taiwan government is considering, which is in a very early exploring stage between governments. You may say there's a possible travel bubble between Singapore and Taiwan in the future but we don't know when. (Linky to another news coverage in English)..Taking into account a very conservative approach the Central Epidemic Command Center (CECC, 疫情指揮中心) has been taking with regard to opening up Taiwan's border control during this COVID-19 epidemic, I don't think any new travel bubble would happen soon.

When do you plan to take this trip? If the first segment of your planned itinerary is still up in the air, I am not sure how you may get into Hong Kong.