I know some of this has been posted here, but I found these fixes in various parts of the interweb.

Thought I would share them in one post for anyone who is having trouble with the game.

My system is a I3 6100, Radeon RX 480 8gb, running Win10

It includes fixes for FPS and Input lag
EAX Sound even on non Creative cards
Put the DLL files in the directory of the game.. you'll need to do this for all 3 games btw so just putting it in one directory won't do.. each game will need it's own copy in it's directory with the exe

If want the fixes in one download I've uploaded it to my google drive here:
https://drive.google.com/file/d/1kouP77iQaZ3kFyxG7KsYosxcgwEd0RY7/view?usp=drive_link

If you want to grab the fixes from the sources then here's the list / notes

FPS/Input Lag fix: (Credit Methanhydrat [PCGamingWiki])
dinput8.dll: https://community.pcgamingwiki.com/files/file/789-directinput-fps-fix/

Although I did still have a few hickups at first, turning on Vsync in game fixed the few remaining stutters.
My theory is the game actually acts up if the frame rate is over 60, my monitor is running at 60hz btw so
this may not work if you have a 120 or 144hz monitor, you might have to resort to trying to cap the frame rate in your video drivers (if possible) (AMD Chill might work for example) or temporarily setting your refresh to 60hz

Widescreen (Extraction point)
Extraction Point does not support setting widescreen resolutions via ingame menu.
You'll have to manually edit the configuration file: C:\Users\Public\Documents\TimeGate Studios\FEARXP\settings.cfg

Look for "ScreenWidth" & "ScreenHeight"

Example my monitor is 1680x1050 so
"ScreenWidth" "1680"
"ScreenHeight" "1050"

Make sure you set your other settings up before modifying the settings file because going into the display menu in game will cause the resolution to reset, you'll have to exit and modify the file again.

EAX Sound (Credit NTU [Steam Forum])
This will enable better EAX sound even without a creative labs soundcard.

DSOAL (dsound.dll): https://github.com/NTULINUX/dsoal/releases/tag/dsoal-01022020
Open AL: https://openal-soft.org/openal-binaries/openal-soft-1.21.1-bin.zip

You'll need to rename soft_oal.dll to dsoal-aldrv.dll

If you're on Win8+ you'll probably need to add registry entries so the game knows what dll to load
Run the game with the DLL's in place and see if EAX is still grayed out before proceeding to the registry edits.

Location1a:
Computer\HKEY_CURRENT_USER\Software\Classes\WOW6432Node\CLSID\{3901CC3F-84B5-4FA4-BA35-AA8172B8A09B}\InprocSer ver32

Location2b:
Computer\HKEY_CURRENT_USER\Software\Classes\WOW6432Node\CLSID\{47D4D946-62E8-11CF-93BC-444553540000}\InprocSer ver32

Location2a:
Computer\HKEY_CURRENT_USER\Software\Classes\CLSID\{3901CC3F-84B5-4FA4-BA35-AA8172B8A09B}\InprocServer32

Location2b:
Computer\HKEY_CURRENT_USER\Software\Classes\CLSID\{47D4D946-62E8-11CF-93BC-444553540000}\InprocServer32

Default value for these needs to be: (Default) = dsound.dll
For me on win10 none of these keys was present prior, location 1a was the one that fixed F.E.A.R for me.
So I recommend you try that location first.

Credit: Various Users [Steam Forum] / indirectsound registry problem help page.
https://www.indirectsound.com/registryIssues.html

In my all in one fear fixes archive I've included 4 registry files 1 for each location which can do this for you
but it's still not a terrible idea to open regedit and check these locations 1st to make sure you're not overwriting anything important.. chances are extremely low that you are but just as a warning im not responsible.

Between these 2 fixes the game ran very smooth for me on my system without stuttering or lag with settings to max @ 1680x1050 resolution, The GPU barely got above idle temps and the cpu utilization rarely got about 20%
I think this game is Dual threaded.. not sure, It worked on all 3 games in the platinum pack

Multiplayer seems to be completely in F.E.A.R and Extraction Point, the game for me at least simply exits trying to go into MP mode.

This game originally had LAN only play as well as user dedicated servers, so theoretically that "SHOULD" still work.. but doesn't

Perseus Mandate has a working MP menu however it complains of CDKEY validation.. My best guess is it can't contact the servers which are long gone to verify the key is legit, either that or GoG has just messed up the install which if im being honest is pretty ugly.

Apparently there is still a working community maintained multiplayer F.E.A.R combat
Which can be found here: https://fear-community.org/
My understanding is it's free but didn't test my self.

Disconnected from Server
This can happen when playing for an extended period of time in my case it was between levels.

It's been suggested that setting the renderer to reset between levels will fix this.
Also you can try patching with a 4gb patcher.. this works because 32bit programs typically only had access to half the address space of 4gb total leaving the other half for the system, but on x64 bit systems each 32bit program can have complete access to the 32bit memory space the full 4gb, I did not test this my self however you can find the patcher here: https://ntcore.com/?page_id=371

I only experienced this problem once, Perseus Mandate late in game when playing straight thru with the render reset off.
Restarting the game fixed the issue.

Reclaiming File Space
You might not know this but the game comes with 1.44gb of BIK video files in the "movie" folder inside the games install directory, these have extra videos that you can also download as "extras" from gog although the ones you download manually are in mp4 format, they're the same content.

GoG does not create a link on the start menu so unless you go looking around you won't even know these are there, the game does not reference these, it's simply extra files you don't even know about.

If you are not interested in them you can delete them to save your self 1.44gb of free space which if you're on a SSD can be precious.

Hopefully with these fixes/tips you will be able to play thru this game which is pretty good and would have been very impressive in it's time.