Yeah I'm sure I botched the timeline.
So I did some research (should have done this the first time), and found this:
https://russellstreetreport.com/salarycap/waiver-rules/
I can't tell exactly how old it is, but it does reference comes of the changes made in the most recent CBA, so it should be applicable to this season. It doesn't account for COVID rules though, so my guess is its from 2018/2019.
Four designations:
1. Healthy player with < 4 years of service (non-vested veterans) are subject to waivers.
2. Healthy player with 4+ years of service (vested veterans) are NOT subject to waivers. Their release is outright and free to sign anywhere
*Note that this only applies until the trade deadline. Post-trade deadline, ALL players are subject to waivers.
3. Injured players with 4+ years of service can go directly to IR. Do not need to clear waivers.
4. Prior to 2018, injured players with < 4 years of service had to pass through waivers before reverting to IR. It sounds like in 2018 this was changed, and now nobody is required to clear waivers prior to going on IR.
*Note that any player placed on IR in the preseason, prior to final cuts to the 53 man roster, can't be designated to return. Their season is over. That's why many of the "shorter term" IR players make it on the initial 53, even if they haven't practiced in weeks or months.
I also found this, which may explain the Hill situation:
https://www.nj.com/giants/2016/09/what_does_it_mean_when_an_nfl_player_is_waivedinju.html
Basically, with a lot of these rookie deals, like Hill's, they're not guaranteed. So when Hill gets injured, depending on his contract, he's not really "entitled" to just sit on IR and collect his full salary. Teams will frequently "waive/injured" a player to open a five day window to agree on an injury settlement. If they agree, the team pays the settlement amount and the player becomes a FA. If they don't, the player reverts to IR.
I don't know if that's what happened with Hill or not, but since it appears he was "waived/injured", it basically sounds like the team was willing to let him walk for an injury settlement, but they couldn't agree to one. My guess would be the Ravens were interested in paying him less and offered him a settlement and an opportunity to join another club, but he declined.
Article even mentions that there's typically not much incentive for a player with a season-long or long-term injury to take a settlement, which makes sense here.