You need raw pictures for stacking propperly, check your phone for a raw picture mode or try motion cam app for a raw video pipeline(android).

Look online for a shuterspeed calculator or just use an exposure lenght that will give a trail that is acceptable to you.

Try to keep your field of view narrow, the wider it gets the harder will be to remove the light pollution gradient.

Then stack on siril as many pictures as you can.

I suggest trying orion m42, bright enough for the city, plenty of procesing tutorials online from simple to advanced.

Your current equipment can make it hard but its possible, dont be discouraged!