However if I wanted to convert all my LTC to another currency like Cardano or Stellar Lumens, there IS no fee.
Fees are different depending on the network the token/coin use. Take USDT token as example. If you use ERC20 means ETH network then you are going to pay a lot like over $20 to move the token from one address to another but if you use Tron netwrok with TRC20 then the fees will be less than $0.50 I guess.
You need to study all these individual networks.
Edit: An additional question I forgot to ask: I'm hearing mentions on youtube comments of people complaining about ETH or LTC gas fees. Anyone know what that's about?
Not sure about LTC but with ETH there are too many projects and recent defi made ETH netwrok too crowded. As far as I heard they are working on lauching Ether 2.0 or something to fix this issue.