
Septerra Core Fatal Panic: "v1.04 Panic: Game has not been properly installed. Septerra Core will exit now." Nothing seems to solve this.
Nothing seems to work.
Me again, but with another machine this time. The "native" version is useless on any machine I ever tried it on, and Proton seems to work sporadically -- on one machine it works, on this one it doesn't. I tried many different versions of Proton and Proton-GE, various settings with winetricks, protontricks, installing through Lutris... Nothing works. Whatever I do, I always get the "Septerra Core Fatal Panic" error stating: "v1.04 Panic: Game has not been properly installed. Septerra Core will exit now." Nothing seems to solve this. I'm not sure if this has anything to do with the hardware. The other machine, where the game works with Proton 8, has both CPU and GPU by Intel. The one I'm writing this report from has them both from AMD. And I see most people complaining on PC have AMD hardware, strangely enough, if we consider that the game seems to work fine on the SteamDeck, which is also AMD-based...

Switched to Proton 8.0-5 (latest stable)
Crashed on me only once, in the first about 3 hours of gameplay. Otherwise feels stable.
Running the game as "native" actually installs an outdated Wine wrapper, which will likely not work on current Linux systems. However, now the game seems to run almost perfectly with a recent version of Proton. I'm using Proton 8.0-5, and I've played the game for about 3 hours, and I've had one crash at the very beginning, which I'm not sure what caused it, but everything seems to work fine now: going in and out of the game causes no trouble, the graphics is as it was back in the day (it is an old game), no stuttering, same with the sound, saveing and loading works as expected, the cut-scene videos work fine... All seems good. I only hope that crash doesn't happen again, or at least not too often.
All older versions of Proton I've tried did have some serious issues, so I recommend using at least Proton 8, which seems to fix them, or newer. But other users might have different experiences.

Removed the layer; moved mouse triggers to L2/R2; higher mouse sensitivity on the right stick
Although the game runs great, I recommend the "Definitive Edition" patch for the best experience with the controller support, which then you can use the Gamepad with Mouse Trackpad instead of what is listed on this report (make sure you set the mouse left trigger as well!). https://www.zombs-lair.com/post/definitive-edition-patcher-septerra-core

Runs better on the steam deck than on PC. The typical bug where it only runs once after install is gone. The small screen of the steam deck is perfect for a game of it's era. The default control scheme steam reccomends is usable. Movies play without issue.
%command% /fullscreen 1920 1080
The game is not really native for Linux. The "native" installation still tries to run the game through Wine, but usually it fails to run.
I've tried all the advices given by both PC and SteamDeck users here, I've tried both "native", and various versions of Proton and GE-Proton, tried to tinker with the scripts, and with winetricks, installed through Lutris -- but found no usable solution.
Resolution was not always reset to default after exiting the game.
On "native" mode, the game runs only the very first time after installation and removal of InstallScript.vdf. After that it fails to even start at all. If I don't remove InstallScript.vdf it fails to run even that first time after installation.
On any Proton or GE-Proton version I tried it fails to run, with a "fatal panic" error dialog stating the game was not correctly installed.
I've bought the game because I loved it back in the day, and now on Steam it is declared it runs natively on Linux, but not only it is not native, in fact it is entirely unusable on Linux, whatever method I tried. It is very frustrating.
Followed Kai's step to delete the install script, but not the step for forcing a different Proton version.
Completely optional, but also enabled FSR with a low sharpness setting, which clears up the text without too much over sharpening.
Reduced right trackpad sensitivity
Haven't played for too long yet, but so far there haven't been any issues running with the default version of Proton included in SteamOS.
Before switching to GE-Proton7.29 the game would crash semi regularly. Usually when transitioning between areas.
I followed Kai's advice to initially get the game to run, this was proir to switching to GE-Proton.
I tried a large mix of non GE versions and they all crashed during stage transition until I tried the latest GE version. It's been solid since.
Note: I have yet to get very far in the game, but so far the expereince has been solid.

Following Kai's post's instructions, with a slight adjustment for storage of steam files on the SD card.
Kai's steps work, not all Proton versions do but the latest version listed above works great.
A pain to setup but seems to work fine now.
Force any proton version (tried with 7.0-2) to disable native version. Start game and wait for it being stuck on "running installation script". Switch to desktop mode and delete InstallScript.vdf in Home/.steam/steam/steamapps/common/Setpterra Core. Afterwards it can be started normally.

Never Finishes Installation, Native Version Won't Launch
Upon attempting to run the game, it stays stuck at "Installing: (step 2 of 2)" and never launches. The native version appears to crash immediately.

Tried "native" linux, proton 6.3-8, gloriouseggroll 6.21-GE-2 and 6.1-GE-2. No dice.
Native linux once started, played sounds and resized my display, but did not show an application in my panel nor display the game on screen. All the proton versions I tried hung on the second step of the 'first time set up' screen. Steam displayed "Running installer script ()", and the pop up window did not name the package it was looking for. It feels like there is probably a launch flag to bypass directx (maybe PROTON_USE_WINED3D=1 %command%
) but I ran out of patience - new report later if I try again and this works.

Proton-6.1-GE-2 GloriousEggroll
When the game starts, desktop resolution change
I tested the native version and proton without success, only starts with proton-ge.
For a 60 hour RPG, I think it unlikely anyone could tolerate the crashes enough to power through the game.
Seems like different versions of Proton are worse when it comes to this.
Crashes unexpectedly, and too frequently.