Separate files for types with no inline annotations possible? What an embarrassing compromise. This is all because Matz explicitly won't allow type signatures in .rb files. I wonder how long it'll be until a hostile fork if he doesn't change his mind.
I've found that if all you can say is "I hate this", you usually don't actually understand the trade-offs.
In the meantime, you have Sorbet available. What's the problem?
Both sorbet and RBS have put huge amounts of effort into bolting type systems onto ruby in ways that don't run afoul of Matz's categorical and in-principle rejection of adding type-annotation syntax to the core language. Both or either of these projects would have much better ergonomics without having to bend to this constraint.
As ruby's user base skews further and further away from the hobbyist market and toward the startups that began in the period when ruby was 'cool' that have now grown up into enterprises, this pressure will continue. If Matz doesn't recant, the two possible futures are:
1. Deep compromise (see Sorbet, RBS) to keep types out of the core language; or
2. A hard fork, or a one-level-up language like typescript.