I was about to recommend the excellent Plugable folding keyboard: https://plugable.com/products/bt-key3xl

I used it as a key part of my software engineer's writing toolkit for the first draft of a novel: https://frequal.com/forwriters/

Unfortunately the Plugable keyboard appears to be discontinued. Perhaps it can still be found used. It is quite impressive. It folds small for travel. The keys travel nicely. The case magnetically clicks into a phone stand. The battery lasts a month or longer. Truly a mechanical marvel.

I only wish I'd bought two.