I had exactly that issue with my conservatory, I am basically broke but I managed a massive improvement that made the room usable all year except the winter. I used a roller on a pole to carefully apply greenhouse glass paint and it massively reduced the glare and extreme heat of summer. Cost about 7 quid for a bottle and it’s done two years so far. It wears off over winter in rain and snow. I did maybe 3 coats or so depending on how thick you make it up. I am pretty pleased overall, it looks ok and the light in the room is still very pleasant to be in
Obviously it makes no difference in terms of insulation but we can use the room way more, plants don’t get scorched etc