According to my experience last week, there were still I-fare(at least for SE asia), but only bookable between Friday-Sunday as Weekend special fare (But I found that it may be fake as I still can book now after the limited period!!)

IIRC, the fare from TPE-SIN was around TWD 12000.

The link still here

For stopover in HKG, the rules are as follow:

South East Asia -
Economy Class :
-->with surcharge TWD1500 allow stopover Hong Kong one time for the entire routing.
Business Class :
-->fares with 6 months validity (Business Standard)- with surcharge TWD1500 to allow stopover in Hong Kong on the return journey to Taiwan
-->fares with 3 months validity (Business Save)- NO stopover