I gather you didn’t understand the rest of the post 
Which refers to this thread - UK REITs in ISAs 🇬🇧 - #15 by Gemhappe
Essentially the blocker being a background mechanism for Freetrade to reclaim the 20% tax on PIDs within ISAs and SIPPs (link shared by another member in the thread linked above) - REIT, dividends and UK tax | Assura