someone explain LTIR like Im 5

CapFriendly's LTIR section says a lot

https://www.capfriendly.com/ltir-faq

Okay, so LTIR is a tool that is most often used within a season when a player gets hurt so you can exceed the cap by the AAV of the player that is hurt. When the season ends, players come off of LTIR and count against your cap as normal essentially. This creates a problem because it limits what you can do with your cap until the LTIR becomes available again in season. Since all teams have to be cap compliant when entering the season the LTIR contracts limit what you can do during the offseason. If Seabrook and Shaw both LTIRetire then the hawks cap in the offseason would essentially be their AAV’s combined minus the cap. So that means any UFA/RFA you want to sign, but can’t fit under the cap before opening day are going to have to wait until the LTIR cap is available (STL & Hoffman)

First, why would Canucks give up a first just so the Hawks could put those players on a non cap taxi squad.c. Canucks would just keep their players on taxi squad. And whose knows in a Covid free league there might not be a taxi squad.
A team can have as an unlimited number of players on LTIR. Of course they have to be medically unfit to play.
Is Toews and his 10m cap hit eligible to stay on LTIR all season?
The Leafs were against the cap last season. Then Reilly and Muzzin got injured. So with that "cap relief" when two 5m were on LTIR, the Leafs were able to go to 23 man roster. The downside was losing their top best Dman just to be replaced by Marincin and Sandin on the ice.

I disagree with that sentence about waiting to the opening day to make those signings. The Leafs went years with two 5m player on LTIR....Lupul and Horton and certainly the Leafs didn't wait to opening day to fill their rosters with another 10m in players.

Canucks decline they aren't trading Podkolzin just to move Eriksson and Roussel