Basically, whenever I try to open the vehicle selection menu thru the default mapping CTRL+G or thru the topbar GUI, the game instantly crashes.

I saw no specific errors in at the end of the log file. Sounds like an unhandled exception.
RoR.log
Even the RigSpawner is affected by this.
I did some investigations and it turns out that a special character like ² and any letters with accents are the suspects.
"²²²²²²²²²²²²²Desperado" Rock Buggy²²²²²²²²²
RoR::ImTextFeeder::AddMultiline (this=this@entry=0x7fffffffe280, color=4293256677, wrap_width=wrap_width@entry=-1,
text_begin=text_begin@entry=0x55555eee6c00 "\"", '²' <repeats 13 times>, "Desperado\" Rock Buggy²²²²²²²²²",
text_end=text_end@entry=0x55555eee6c42 "") at /home/babis/Downloads/ror-dependencies/rigs-of-rods/source/main/gui/GUIUtils.cpp:75
75 unsigned int c = (unsigned int)*text_pos
```#0 RoR::ImTextFeeder::AddMultiline (this=this@entry=0x7fffffffe280, color=4293256677, wrap_width=wrap_width@entry=-1,
text_begin=text_begin@entry=0x55555eee6c00 """, '²'
text_end=text_end@entry=0x55555eee6c42 "") at /home/babis/Downloads/ror-dependencies/rigs-of-rods/source/main/gui/GUIUtils.cpp:75
override_alpha=override_alpha@entry=1, wrap_width=wrap_width@entry=-1,
line="\"", '²' <repeats 13 times>, "Desperado\" Rock Buggy²²²²²²²²²")
at /home/babis/Downloads/ror-dependencies/rigs-of-rods/source/main/gui/GUIUtils.cpp:238
at /home/babis/Downloads/ror-dependencies/rigs-of-rods/source/main/gui/panels/GUI_MainSelector.cpp:176
at /home/babis/Downloads/ror-dependencies/rigs-of-rods/source/main/gui/GUIManager.cpp:486
at /home/babis/Downloads/ror-dependencies/rigs-of-rods/source/main/gui/GUIManager.cpp:243
at /home/babis/Downloads/ror-dependencies/rigs-of-rods/source/main/gfx/GfxScene.cpp:241
at /home/babis/Downloads/ror-dependencies/rigs-of-rods/source/main/main.cpp:765
````
@WillyB1337 Good spot, thanks!
Turned out to be one-line mishap, fixed in upcoming PR #2630.

The issue of specials characters is also happening with the chat system. Whenever I try to send a message containing a letter with accents, instant crash.