If you want to follow Twitter accounts from Mastodon, there's a bridge called Bird.Makeup that still works and is working on a workaround to this issue.
I'm working on a Mastodon client called Agora that integrates this bridge into the search, so that if you search for "elonmusk@twitter.com" it automatically loads the bridged Mastodon version of the profile: https://agorasocial.app/#/andrew.masto.host/a/111844567849084915
You can find some solid open source alternatives here, the ones I like most are Lawn Chair and Kvæsitso:
https://alternativeto.net/software/nova-launcher/?license=opensource