I don’t think so.
Apple has had record Mac sales for the past two years, since the release of Apple Silicon.
There’s no way wether or not any one particular website renders as expected is going to meaningfully impact Mac or iPhone sales.
Sure, Apple would prefer that users stick with Safari but they’re not going to lose any sleep if customers use Chrome/Firefox/Edge or whatever else on a new $2499 MacBook Pro.
It’s certainly way more in Reddit’s or other big web property best interest to perform well for Safari users, especially on iPhones and iPads where all browsers use WebKit as their rendering engine.