Well ...
1.5 litres of water
Rule 6 - you should be drinking a minimum of 2 litres
Muesli (small bowl with oat milk)
Muesli?! That's incredibly high in carbs. Obviously I don't know which brand you're buying, but Jordan's Natural muesli is 68g carbs per 100g. And oat milk is higher in carbs than dairy milk.
Falafel salad (with lettuce and beetroot)
Falafels are made from chickpeas or fava beans, so are also very high in carbs. Ditto beetroot - it's not forbidden, but it's in the amber range on the veg carb counter.
Meatballs with tomatoes, beans and red peppers
Skyr yoghurt
Very small glass of red wine (1/2 a glass)
If you're worried about the weight gain, it's probably worth knocking this on the head for a few days!
Friday
1.5 l water
As above
Several coffees with oat milk
Is there a reason you're not using dairy milk? Oat milk is around 7g carbs per 100ml, whereas whole milk is 4.7g. Might not sound like much of a difference, but if you're having several cups, then that will soon add up.
Rice crispies
Really?!!! Even worse than muesli, at 86g carbs per 100g
Chicken salad with lettuce, sweet potatoes and tomatoes
Sweet potatoes have more carbs than white potatoes - depending on if it's baked or just the flesh, this is around 22-29g carbs per 100g
2 Babybels
Yoghurt and raspberries
Thursday
1.5 l water
As above
3 coffees
Yoghurt and strawberries
Banana
And again, banana is the worst fruit you could choose - from a low carb perspective - 19.3g carbs per 100g
Sausage salad - large
I assume that these are low carb sausages?
Yoghurt and granola
Granola is almost as bad as muesli - depending on the brand - around 60-65g carbs per 100g
Missed dinner (sea swimming)
Glass of Prosecco
As per the red wine!
I think, looking at what you're eating and drinking, it's fairly clear why the weight loss is slower than you want - and that you've gained weight.
You really need to ditch the cereals. If you want a low carb granola, there's a lovely recipe in the Low Carb recipe section (I think it's in the vegetarian topic).
You also need to be really clear about the carb counts of the veg/fruit that you're choosing - and definitely need to knock the bananas on the head!