When was the last time they added drm free games?

No idea, i haven't bought there for a long time. Reason for that is the amount of steam keys and the lack of choice in that regard.

That would be:
- The King's Bird
- Overload
- Before I Forget
From the very monthly bundle you are discussing.

And before that, the Bundle for Racial Equality had a number of drm-free games. And before that the Humble Indie Bundle 21 did too (and those are just the bundles I bought, I don't know of others).

As downhill as it has gone, Humble still has bundles and games offered DRM-free. I personally DO blame IGN- I've been buying HIBs since the beginning, and 21 was the first one where not every game was DRM-free and available on linux (there were 2 or 3 that didn't match those requirements).

wonderful monthly this time around.

Nobody post them so I'm gonna do it

Vampyr
Hello Neighbor or Hello Neighbor Hide and Seek Collection
Wargroove
Call of Cthulhu
Little Big Workshop
Genesis Alpha One Deluxe Edition
Automachef
Through the Darkest of Times
American Fugitive
The Coma 2: Vicious Sisters
We Were Here Together
A Case of Distrust

This month only, Premium and Classic subscribers get ALL 12 games! Plus, all Humble Choice subscribers get not one but two new Humble Original games, Booth and Zodiac XX. Subscribers also get an exclusive demo of the new Humble Games published game: Wildfire.

Bonus game for last month is Vikings - Wolves of Midgard

Feel free the toss me your spare keys if you want to cheer me up =)

is bonus game offered as steam key or drm-free content?

Pretty decent bundle overall this month.
Wargroove feels a bit cheap bc it was given away for free b4 and Vampyr is rather meh i guess.
Personally for me it was worth for Call of Cthulhu, Through the Darkest of Times, A Case of Distrust and We were here Together

Strange selling tactic of "Buy in now, get less later". They'd do better to just offer specific plans the option to have all available titles. Instead they seem keen to likely bleed out slowly on this thing until someone breaks the news that it'll be rolling off into the sunset.
Reading posts elsewhere, it appears Wolves of Midgard is a Steam key only. Assuming that's the game you were asking about.

yes, I was.

Humble Monthly for September

Golf With Your Friends Caddypack Collection
Generation Zero®
Forager
Vampire The Masquerade: Coteries of New York
Fun with Ragdolls
Lethal League Blaze
Strange Brigade
Evoland Legendary Edition
Yooka-Laylee and the Impossible Lair
Catherine Classic
The Occupation
The Shapeshifting Detective

Premium and Classic subscribers get ALL 12 games
All Humble Choice subscribers get a new Humble Original game, Alt254 and an exclusive demo Carto.

I've long since unsubscribed from Humble;s emails (and was never subscribed to the monthly bundle), but they sent me an email today. (inb4 fishing: yes it's them)
In Russian.
In which they graciously give me a coupon for the privilege of paying them $15, and threaten me with law enforcement if I trade their shitty coupon on the internets.
Burn, loot, murder, but don't go around trading our coupons.

Yikes, still continues to seem dire for Choice's future.

What is that, almost all repeats from previous bundles on top of being Humble published games?

I was like, oh there is one game from my wishlist, and one that seems interesting, only to realize that all other 10 seems crappy for me.

Oh well, maybe next month.

The uninteresting selection, their attitude towards customers simply gifting coupons or games they don't want are going to dig a grave for themselves. If I only find an interesting game, if any, and I can't even gift the others...oh well.

October 2020’s Humble Choice

Tropico 6 El Prez Edition
Autonauts
The Sunless Bundle
Shadows Awakening
Fae Tactics
Fantasy Blacksmith
The Suicide of Rachel Foster
Goat of Duty
The Uncertain
Basement
Iron Danger
Lightmatter

Premium and Classic subscribers get ALL 12 games, all Humble Choice subscribers get a new Humble Original game, Fate of Kai.