I modified the original 3D model from the level select screen of CELESTE to make it 3D printable. The model of the photos isn't alike the final model, which I fixed after seeing some problems. In print settings and post-printing, I will talk about all the process.
 

Print settings

0.1 or 0.2 layer height. White PLA filament. I reccomend using a low percentaje of infill with a pattern which cover up a lot of space with little material (like line or gyroid patterns). Most of the model doesn't need support material, but some details may fail without supports. Automatic support will make a lot of unnecessary supports, so you should use custom supports. If something fails and you don't want to repeat everything, you can cut that detail from the 3D model and print it separately. I printed it at 190 mm lenght, but you can print it even bigger. Print the aerial tramway separately at the same scale you printed the mountain.
 

Post-Printing

I used a 3D pen for the post-printing process a lot, like for filling holes, pasting the parts that I printed separately (because they failed) and creating some objects, like the cranes and some trees.
If you didn't used a custom support for the flag, it should be just the flagpole at the top of the mountain. Stick a small red fabric to the flagpole to make the flag. For the cranes, I used the 3D pen, but you can use some 3D model from internet too.
Use a thread or a wire for the aerial tramway cable. The aerial tramway has a ring to hook it to the wire. The rings indicate where each end of the wire must be: use the rings to hook them up or stick them with a 3D pen or glue.
I used acrylic paint and I painted it based on the original level select screen of "Celeste".

3D models I used

Celeste Mountain: https://www.thingiverse.com/thing:3943800
Flag with flagpole: https://www.myminifactory.com/object/3d-print-flag-with-flagpole-44199
Snow-covered fir tree: https://www.thingiverse.com/thing:2722279