You can make mastodon have a somewhat more similar feel to lemmy, if you do the following:
Go to preferences > appearance and activate ”advanced web interface". Now if you do a search for a hashtag it will pop out a new column in the interface that you can now also pin, to stay. And in that column's own settings you can now add multiple additional hashtags that will all display their results simultaneously in the same column.
So now it's like as if you have a home feed of multiple hashtags, the feed is topic based, and not person based, and in that sense, more similar to lemmy. It gets very laggy tho if you add more than 5-ish tags, the backend code is not designed for that.
On your phone you can do the same, if you use Tusky. Just add a hashtags tab, and add multiple of them there. But not too many.
Lemmy, however, is the only one with upvote based sorting, and truly designed for the general reddit feel.