This is likely going to be the answer, yeah, but I believe we need to see some improvements in installability for the average person - a window AC unit does afaik not require a specialist to install, while a mini split, while possible to tackle for a handy person, is a lot harder, leaving the average person to have to pay for someone to install the unit.
Window ACs are not the best from an efficiency perspective, but they do beat portable units by a large margin.
EDIT: looks like it might actually not even be legal in the EU to install a mini split yourself - you need to be certified to handle the refrigerants.
Installation is also more than 50% of the total cost of acquisition, so we’re hitting upon an affordability issue here as well.