I'm looking for a lightweight stroller with 25kg weight limit and also a high backrest, what would you recommend please?
Do bear in mind that lightweight strollers are, well, lightweight which means smaller, less spacious, less durable in order to achieve the low weight and foldability they offer. Even if claiming 25kg weight capacity they are better to be used with lower weight and more occasionally, compared to larger, e.g., three-wheeled or all-terrain strollers that are meant for more strain.
From the lighter strollers, I would absolutely go for a Baby Jogger City Mini 2 or, better yet, a Baby Jogger City Mini GT2. A mid-size stroller, I know, but a lightweight at that and much more durable, considering.
Next in line, I would consider an Uppababy Minu (I know, 22.5kg capacity but I feel like it's enough for such a small stroller), or a pre-loved Baby Jogger City Mini Zip would hold the weight well. I would also consider a Quinny Zapp Xpress, a nimble one that can hold a larger child even if claiming a lower weight maximum - I could fit a 4yo in there just fine...
And from the really small ones, maybe a Chicco Goody Plus (not that high of a backrest but enough space to the canopy) or a Cybex Eezy S+2 (a higher backrest but still, I feel like maybe not so spacious for a 25kg child).
Again, it's all about priorities when choosing a stroller, and if that is weight capacity, you should go for a larger, quality one - like a Baby Jogger. If it's smallness, count on a smaller space and fewer features and sturdiness.
And it's not really about the weight capacity on paper at all. Actually, even 15kg capacity strollers of quality can hold much, much more. On the other hand, many pushchairs claim high weight capacity but cannot hold such a large child by far. And the very cheap strollers claiming 20+ kg maximum load often get rattly soon because of that... So it depends on much more than just what the manufacturer claims.