So I was watching the WR Steam scriptless run, but he's bhopping like it's an older version. If I'm correct and he's on the latest steam version, how's it possible?

ok i have a step by step tutorial on how to bhop:

step 1: you just bhop lmao

step 2: if steps unclear revert to step 1

You can bhop on the steam version just like on WON but every few hops you have to ducktap to not go beyond the speed cap

you can b hop by bunny hopping EZ

@JKRZJKRZ what does ducktap mean?

If you have a "bind mwheelup +duck" or "bind mwheeldown +duck" bind and you scroll up or down, depending on the direction you bound it to, you're gonna duckroll.
You can ducktap by scrolling the wheel by just 1 step which will input a short +duck that looks like a tiny jump.
Or you can just duckroll for a short ammount of time. The most important part is to lose some speed after 2-3 hops so you won't get stopped by the speed cap.

TLDR ducktapping/ duckrolling can help with doing small amounts of movement without losing that much speed.
this is achieved when you spam crouch/duck (with mwheel) after bhopping, you can move small amounts. it is used if you know that you wont be able to land that far with a simple b hop, and if you do b hop, you will go too far.

Also is there a tutorial for the unmodded Steam version?

umm.. if you own the steam half life version, i recommend you get the goldsrc version, because it has a speedometer, a bunch more customization, and uncapped speed limit. https://www.speedrun.com/hl1/resources
this is the link to the files.
Pick the GoldSrc one.
if you are interested in just the steam version, there porbably is some stuff about it in the guides section.

So I was playing with the Tau Cannon and I noticed that if I kept duckrolling I wouldn't lose the speed but I also couldn't jump. Is there any way to jump and not lose speed?