My fight against enshitification entails hand-delivering paper correspondence by bicycle. I also re-use the windowed envelopes that I receive. When I run out those, I leave the envelope unsealed so the recipient can easily reuse the new envelope.

The recipient generally must use the postal service to reply. And rightly so. Penalizing them with the cost of printing and posting serves as a means to punish them for the enshitified digital path they offer. For me, this approach sufficiently casts my anti-enshitification votes while supporting the postal service that gives refuge from enshitification, without excessive environmental detriment.

The LaTeX scrlttr2 class is useful for using and re-using windowed envelopes. If the envelope is standard, the geometry may be known to the supplied KOMAscript machinery. If not, a few measurements can be given as parameters to align an address in a custom window.

To load the US №9 standard envelope, you would start with:

\documentclass[UScommercial9]{scrlttr2}

or for the French standard:

\documentclass[NF]{scrlttr2}

If you reuse a non-standard windowed envelope, you can put the following in the preamble and tamper with the measurements as needed:

\makeatletter
\setplength{foldmarkhpos}{4.2mm}   % default=3.5mm; distance from paper edge to fold mark; should account for the unprintable area of your printer
\setplength{tfoldmarkvpos}{108mm}  % default=99mm; distance between top fold mark and top paper edge
\setplength{firstheadwidth}{190mm} % default=170mm for NF and \paperwidth for others; width of letterhead
\setplength{firstheadvpos}{10mm}   % default=15mm for NF; distance from top edge to letterhead
\setplength{toaddrvpos}{40mm}      % default=35mm; distance between top of window and top paper edge
\setplength{toaddrhpos}{98mm}      % default=-10mm; distance from the left edge of the paper to the address field (if positive)
\setplength{toaddrindent}{5mm}     % default=10mm; left and right indentation of the address within the to-address box
\setplength{toaddrheight}{40mm}    % default=45mm
\makeatother