Single panel or two panel, one top one bottom, were popular.

Like this?

The 20’s to the 40’s is a broad range- covers everything from late arts and crafts, deco, all the revival styles like Dutch colonial etc, into modern styles with slab doors. Is there a particular reason you are aiming for a door from this era? A restoration or new construction or?

What style is the house?

My original 1928 interior doors

Ooh I love the look of these! Beautiful pendant lights too. I guess I should also ask what style knobs… we are renovating a house and trying to keep it older

Also, the house is a cottage style

I have glass knobs on brass plates.

The standard 6 panel door has been used in the US since the 18th century, there was really no era it wasn't used, at least in a certain quality of house, and it didn't really matter what the style of the house was, because styles got mixed together and even though it was a "traditional" or "Colonial" door, it would be used in houses that were not. Even some of the midcentury houses in my area have this style of door because I live in a colonial city, and they frequently used colonial details in other eras.

The 1920s to 1940s houses where I grew up often had the two panel style I show below with hardware in a sort of deco shield-like escutcheon or a simple round one and glass knobs. The one neighborhood I lived in had rather flimsy two panel doors, but one of the fancy houses I knew of, which had been remodeled in the 1930s or 1940s just had nicer version of the same.

My 1932 house has 3 panel doors. Most have glass knobs, but the knobs on the inside of closet doors are metal.

I set all my antique glass knobs outside in the sun for a month and turned all the glass purple. I did them all in shifts.

WOW that is quite span in style of homes as Hallett stated. Can we see your home ? Are there no doors to get some clue? Waht is your style ? IMO the doors should suit whatever style you are going with inside I hve never thought the inside needs to match the outside of a home. So at least post pics here of the home and some idea of your style. I went to your idea books not much hint there as to style.