Mastodon includes an optional feature which lets you automatically delete your posts after a certain amount of time. There's a guide to using this feature including lots of questions answered at:
➡️ https://fedi.tips/deleting-posts-automatically-in-mastodon-after-a-certain-time-period
It's off by default, it only deletes stuff if you switch it on. You can also set it to keep certain posts, more info in the guide.
I've tried to answer questions about this feature in the guide, but let me know if I've missed anything.
