Supervised Solo requires exercise of the FI privileges so the hours count towards the 25%.
Not so. See FCL.1005: Limitation of privileges in case of vested interests of Regulation (EU) 2019/1747
Examiners shall not conduct:
(a) skill tests or assessments of competence of applicants for the issue of a licence, rating or certificate to whom they have provided more than 25 % of the required flight instruction for the licence, rating or certificate for which the skill test or assessment of competence is being taken;
Which means for a PPL course, it's 25% of 25 hours, i.e. 6h 15 min, no matter how long the applicant takes to meet the Skill Test entry standard.