Nice! If you need more mods I'd be happily up for it. I've never set a PB because, well I don't get out of Highlands all that often if I go fast :P
You'll have it if you can launch scripts. Not sure how you do that though. If you have it installed via the Unity port or Android port or something then I don't think you can unfortunately.
Try verifying the game files and the usual Steam trouble shooting steps.
On Windows you'll want to just open Notepad and save the file as "record.bat" and run that.
Read this: https://dsdarchive.com/intro and it'll tell you how to do the demos.
If you have the shareware version then you can only submit for the first episode, as you can't play the rest.
If you got "FreeDOOM" then that's a different game, so you'll have to submit that elsewhere (there's a section in the Doomworld forums for it)
If you "pirated" or """legally acquired""" the game, then you're good to go, just don't tell Bethesda.
https://www.speedrun.com/quake/guide/s25n6
And the rules for whatever category you want to run
So I asked this on doomworld, but bad timing, and I got burried.
https://www.doomworld.com/forum/topic/117885-rta-speedruns-on-hurt-me-plenty/
(The title on doomworld is bad, it should be Non-RTA)
This is the general route, getting around the monsters is just something you learn after.
Watching the individual level records can also help (although sometimes there's 1 in a bajillion jumps and cuts that you'd never make in a full game run)
DSDA moved to M8 timing a while back due to most sourceports having that timing and it making it simpler for new players who are certainly using a sourceport that can do M8 timing.
On Mac you run the cli version of the timer. Same for Linux. The GUI version is Windows only.
From your terminal on Mac or Linux run java -jar timer_cli.jar
and follow the on screen instructions.
As for who uses Llanfair? I do, because it has global hotkeys on Linux where everything else that runs here I've got to be tabbed into which is pretty tough for 30s levels in DOOM and Quake :P