Joerg wrote:

Just received a new rear wheel. Despite being 700c and for narrow tires
the rim is drilled for a Schrader valve. Couldn't believe it. Harumph,
grumble. Why on earth ... well, it is what it is.

I can't imagine what your objection could be, given that Presta valves are inferior in every single possible way to Schraeder valves, except for their diameter. Count your blessings and use a better, less fault-prone tube.

It confounds me to come up with a rational explanation for why the recent crop of big wide rims (including fatbike rims) are mostly drilled for Presta valves.