The big things are sound and video driver support.

For Win98SE, you can go as high as GeForce 7xxx

But for DOS sound, you are much more limited and will most likely need a PCMCIA sound card.

There's a rough spot in the laptop chronological continuum... years 2005-2008 were very badly affected by failures of immature lead free solder processes, either at the chip supply level or system integration level... anything you get from those years that happens to still be working through some fluke, may suddenly die on you. Well it's all old, everything may suddenly die on you, but these have the life expectancy of a 110 year old diabetic smoker with cardiovascular disease, who just pissed off several organised crime syndicates at once. This roughly coincides with the advent of dual cores and windows vista. Past 2008 you're getting very unlikely to have Win98 drivers for major components, 2005 or earlier, you're looking at Turion64s, P4M 2.4 etc as fastest. However, it's not all roses without thorns pre-2005, backlights seemed to only have a 3-5 year lifespan, and closer to 2000ish, it seemed like everyone forgot how to build hinges.

Edit: Maybe lead free solder probs lasted longer than that, it just occurred to me that we had an i7 mobile desolder it's chipset, that was a 1st gen, must have been 2010 or 2011.

I have a Toshiba laptop that sports a regular Pentium 4 CPU and has a GeForce FX Go 5200.

Fine for 98, but DOS sound is not there.

I got a HP NX6125 fully working with Win98SE and ME, but I needed a different WiFi card which made me have to install a modification to the machine since it uses a whitelist and video driver had to be edited with new ID to make it support the ATI video in the chipset. I don't think it will be easy to get something fully working much past that era, there simply won't be any driver support for most of the hardware in the machine.

Maybe a ThinkPad, the T42 should be the last to support windows 98. IT runs a Pentium m which is kind of cool. Its Also the last thinkpad made by IBM. I have never owned one though and can't speak if it's gaming capabilities, should be a lot of YouTube videos of it as it seems common.

Joakim wrote on 2021-07-05, 20:14:

Maybe a ThinkPad, the T42 should be the last to support windows 98. IT runs a Pentium m which is kind of cool. Its Also the last thinkpad made by IBM. I have never owned one though and can't speak if it's gaming capabilities, should be a lot of YouTube videos of it as it seems common.

I have a T42 (Pentium M 2.0GHz, Radeon 9000) that I pair with an IBM Dock II. The laptop itself runs Windows 98 really well, and I put an Aureal Vortex (sometimes with a Dream Blaster S2 for MIDI) in the Dock II for DOS. It makes an excellent retro rig. I also love the T42's screen.

The Dell Latitude D600 works as well. It has almost exactly the same specs as the T42.

Joakim wrote on 2021-07-05, 20:14:

Maybe a ThinkPad, the T42 should be the last to support windows 98. IT runs a Pentium m which is kind of cool. Its Also the last thinkpad made by IBM. I have never owned one though and can't speak if it's gaming capabilities, should be a lot of YouTube videos of it as it seems common.

Depends on the specific model. I'd really like to have one with the highest available specs. I think it's Mobility Radeon 9700 or maybe 9600. The latter exists, I know. Sadly whenever I see one it's a Mobility Radeon 7500 or 9000.

It's just sound finding a laptop with something decent video wise isn't a problem

Do you really need dos or at least dos sound? as the laptops your already looking at will have dropped soundcard support in dos. Even by the P3 era a lot of laptops had dropped this.

We use to use IBM Thinkpads at work.
Very good laptops and easy to fix and upgrade.
I ended up buying one for my personal laptop.
Very reliable. Don’t forget to get the Dock.
We ran Win-2000 but they support Win-98 too

Thinkpad “T42 and T43” series
Thinkpad “A21” series

I've got one of these, and would recommend it on the basis that it still works. https://support.hp.com/ca-en/document/c00351201 and that you can swap between optical drive and floppy drive in the multibay. You only get DX7 hardware though. DOS sound may be got working by... VIA AC97 DOS Drivers?