Mastodon's web interface has a special optional "advanced mode", which is designed for people on computers who want to view several timelines at once. Here's a complete guide to using it including how to switch it on and how to add columns:
➡️ https://fedi.tips/how-to-activate-mastodons-tweetdeck-style-advanced-web-interface
You can use it to have dedicated columns for timelines, accounts, hashtags, lists, bookmarks, favourites, DMs etc.
(If you used to use Twitter, it looks quite similar to the Tweetdeck interface.)
