The EU Commission published their Q&A regarding the EU Taxonomy Alignment Reporting for Financials.
As anticipated, the question regarding full vs. split premiums for the calculation of the share of taxonomy-alignment is part of this FAQ: you can find it on page 48 (question 67). The EU Commission clarifies that only the relevant share of premiums should be used to calculate the taxonomy-alignment of insurance undertakings:
“Insurance undertakings should use those insurance premiums, or corresponding shares of insurance premiums in case of multi-risk insurance contracts, that only pertain to the coverage of climate-related perils for the purpose of computing Taxonomy-alignment.”
Insurance Europe position paper on EU Taxonomy Art. 8 Q&A