Good day tomasio,
hmm currently some "merge" feature do not exists in Locus so import is a best method. You may simplify import by packing all GPX files you want to import into one folder, into ZIP file and import this ZIP. I'm sure, it will be a lot faster

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If you do not have tracks in GPX, there is need first to backup current database, restored old database, export all tracks to GPX, restore new database and import all GPX files ... uff complicated, sorry.
EDIT: and thanks for offer for graphics works. There is always a lot of work to do, but I mostly welcome some "interest without request"

. So if you find something in Locus, where you are sure you may do it better (like any icon), feel free to write me specific suggestion. I'm cooperating with one freelancer that did most of complicated graphics in Locus, but because of his lack of time, I learned basics in PhotoShop so now I'm most of simple icons do by myself ... which is not optimal solution ...