In my prime SLR days (1970s-1980s), my standard kit was a 35/85 lens pair (mostly Nikkors, although I did have a Contax for a time, an Olympus for a time, etc). A 21 and a 200 were also in the kit for extreme moments, but I only rarely carried them. A 50-ish macro is another "always in the kit, not the most used, many of the best photos" lens for me.
With Leica RFs (only had a couple others over the years, mostly fixed lens) the 35 and 50 have been the most frequent, and it's a flip-flop between them as to what I'd pick if I NOW had to decide on just one. I'm finding again that a 35/75, or 28/75, works well for me, and of course I have focal lengths down to 10 and up to 360 mm available for the occasional moment.
(A 20-21mm is fun and easy to use, a 10-15mm is difficult to get my head around. Likewise a 75-90 is fun and easy to use, and longer takes serious work.)
G