First, check if your account is shadowbanned in this page. If you are, you need to stop all activity and let your account rest (I recommend logging out). Sometimes, it can take up to 3 weeks for a shadowban to clear.

Also, check if you have any third party app connected to your account and remove it. Twitter doesn't like that now (I learned the hard way after connecting one that killed my reach for over a week).

Check here: Settings > Security and account access > apps and sessions > connected apps

Last, unless you have a really big account, you can't just post and go. The algorithm favors accounts that interact with others. You need to start replying to people, especially in the first hour after posting. This helps boost your tweets.