I've built a microsite called slow.fyi. It is a single-purpose, small, and simple page designed as a shorthand anyone can use to declare that receiving a reply would be appreciated (rather than being expected).

This has seemed really important to me now the stresses of our own lives are unpredictable, let alone those of our friends we're not regularly in touch with. I've been using "slow.fyi", written literally like that in Signal, Whatsapp, emails and similar, as a way to demonstrate a lack of pressure in long or short messages I've been sending to friends. Perhaps you'll find it useful too.