This post below from @ojblanchard1 neatly explains why the ECB introduced the TPI (Transmission Protection Instrument).

This program is far more discretionary and opaque than its predecessors, OMT (Outright Monetary Transactions) and PEPP (Pandemic Emergency Purchase Programme), with no ex ante limits on bond purchases and far less transparency about the policies underlying its activation. The moment France, with debt well above 100% of GDP, structural budget deficits of around 5% of GDP, low — via @jsblokland

ECB's discretionary, opaque TPI lacks ex ante limits, signaling systemic policy shift.