I know this sounds ridiculous, but AFAIK there is no way to merge two photos together on Android without using proprietary software filled with ads and trackers, or paying money. None!
What do I mean by merge? I mean: Taking one photo/image, arranging it beside another image, and exporting them as one single image.
I usually do this task on desktop, but a few times a year I have to do it on mobile, and the options there are so bad, it’s shocking.
Please, someone make a FOSS app for this!
I’ve encountered the same need as you, but I haven’t found anything either.