In case you missed it, all links on Mastodon count as 23 characters towards your limit, no matter how many characters the link really is.
So, you don't need to use link shorteners on Mastodon as they won't actually affect the link's length.
Mastodon does this because it's better for everyone's privacy to avoid link shortener services, it means people can see what they're clicking on, and the link won't stop working if the shortener service shuts down.
More info at:
➡️ https://fedi.tips/you-dont-need-link-shorteners-on-mastodon/