A recent thread that you might find interesting.

Good overall 40c gravel tire

3x inner width max is as far as i would go.

Your wide rims, at 25mm outside, 21mm inside, will fit a wide range of tires.
I assume you have disc brakes? (Or cantilever brakes, perhaps?)

It sounds like you are looking for more puncture protection from sharp stuff, which will affect your tire selection. Strong puncture resistance often makes for a harder riding, slower tire. Knobs for loose surfaces will also slow you down.

The GP 4-season tires should do okay offroad, if the surface isn't too loose. They have some tread grooves. But a wider tire would be good.

If you are hopping curbs and slamming potholes, you'll want more air pressure than I use.

~~~

I have the same width rims, HED Ardennes+, measuring 25.5mm outside, 20.6mm inside. These are "tubeless compatible" (I use tubes), so the tire bead kind of snaps into place when I first inflate them. I'm not worried about very narrow tires possibly pulling out of the rim when the bead is secured like this.

I'm about 170 pounds.
On my road bike, often on fast-for-me group rides:
23mm Continental GP4000S, which measure 26-27mm on these rims.
80 psi front, 95 psi rear. I'll add 5 psi to each if there could be bad potholes or rough RR tracks.
A fast ride, with lightweight tires. Yes, the tires are only a couple of mm wider than the rims.

On my gravel / all-day ride bike, I've used:
25mm GP 4-seasons, measuring about 29mm on these rims.
65 psi front, 80 psi rear. A smooth ride on chip-seal or tar strips. These have an extra sidewall layer, so they aren't quite as flexible as the GP4000S, but should be better on sidewall cuts. (But I haven't cut either one for 3 or 4 years, now.)

35mm Clement USH, no longer available? Clement is now Donnelly and has some new tire models.
These have a solid block tread down the middle, to be faster on pavement, and small knobs on the side.
(not sure of pressures now, maybe 50 psi front, 60 psi rear?)
These rolled reasonably well on pavement, and did well on gravel. A good compromise on a mixed paved and unpaved ride. I did slow down on fast downhill paved turns, since I didn't want a chance of losing traction on the side knobs.

38mm Compass Barlow Pass, measuring about 39mm on my rims. These are smooth, with a subtle file tread, and thin flexible sidewalls like a road tire.
Heavier, at about 400 grams, compared to 190-220 for the 23-25mm road tires, and the larger tubes are heavier, too.

But the ride is quite amazing at 38 psi front, 45 psi rear, just floating over very rough roads. There's essentially no local gravel to try, I'll ride these out of town this year. I'll test about 33 psi front and 40 psi rear for offroad rides.

I got these for fast, efficient riding on smooth crushed stone rail trails, and on gravel rides. But they turned out to be quite fast on pavement, very similar to my 25mm GP 4-seasons. I'd like to do a back-to-back test this year.

These were very nice on a long road ride with partly smooth roads and partly new rough chip-seal. They did fine on a few short stretches of loose gravel, too. Very good steering response for such a big tire. The fat contact patch makes them feel very connected on turns, a lot different than side knobs on offroad tires.

They are supposedly quite good on puncture resistance, due to the low air pressures, even though there's not a lot of puncture layers. For mostly paved riding, I'd consider the 35mm version, just to save the 100 grams per tire.

Has anyone seen these or have a copy of the old versions?

Appreciate all the responses.

Glad to hear my repetitively new wheels will support a wider tire.