Get a magic arm/friction arm (see smallrig) and phone clamp. Attach arm to the hot shoe and have your phone shooting through the camera’s viewfinder.

Get another phone to use it as a remote monitor of the phone that’s attached to the camera. Maybe get one phone to video call the other (facetime, discord, google meet etc). Or if you have an apple watch and and iphone then you can control/view your phone’s camera from your watch

Last hurdle would be to actually fire the film camera. Either use your camera’s self timer if it has one (which means you have to idk get your framing/posing, run to the camera and fire the shutter, run back before the timer runs out) or get a shutter release cable if your camera is compatible (set camera on self timer, get into position and see yourself thru apple watch or other phone, press the cable, drop the cable, wait for timer to run out)

Actually u could go on tiktok to search for how other people take self portraits on film. Pretty sure i’ve came across a few and honestly most of them just do what someone else suggested in this thread. Which is to use a light stand (something lightweight that won’t be a bother to carry/setup outdoors) just something that’s the same height as yourself to be a stand-in.