Tips/commands for higher fps

Gmod is very CPU intensive, so having a good cpu will improve fps a lot.
RDR2 on the other hand, if I know correctly, is a GPU intensive game.

What CPU do you have?

I've found that this autoexec config (taken from: https://perpheads.com/threads/perpheads-performance-guide-2024.60890/) helps with fps quite nicely:

cl_burninggibs 1
cl_new_impact_effects 1
cl_threaded_bone_setup 1
fps_max 0
gmod_mcore_test 1
mat_picmip 10
mat_queue_mode 2
mat_specular 1
menu_cleanupgmas
m_filter 0
mp_usehwmmodels 1
m_rawinput 1
r_3dsky 0
r_shadows 1
r_lod 2
r_queued_ropes 1
r_radiosity 4
r_rootlod 0
r_threaded_particles 1
studio_queue_mode 1
host_writeconfig

Optimise your game to match your hardwares capabilities, not underperform to what your CPU is capable of. This is usually the issue for a lot of people who use configs to minimise everything. If your graphics settings are too low, it creates a bottleneck effect.

As Gmod is CPU Based, ideally you'll want to ensure you have a good CPU, using multicore rendering, and that your settings reflect your computers capabilities rather than making the game run on dell laptop mode.

Make sure gmod_mcore_test 1 is on and that you're running the x86-64 chromium branch of Garrys Mod (if you're using a 64 bit computer of course), and that you're only running the addons the server needs and what you plan on using whilst on the server.