I'd expect that his thinking on reading the PR is that this code is OK, but could be improved by doing such-and-such, I'll do that later. i.e., he doesn't see it as rewriting but just as incremental improvement (and as such would be out-of-place as a PR comment). Ask him if he could put those ideas into PRs, as a learning opportunity for you.

So you know what you want him to do, and you are asking for advice to get that to happen. So I imagine that you want to learn how to stop your team lead changing the code you contributed after you contributed? Or do you want to do something else?

It helps to literally write out your own desires and wants of things that you can do yourself (versus other people doing) when it comes to these types of situations.

For example in a similar situation I might say "I want to make a case to my manager that the team lead isn't treating me fairly" or I might say "I want to be less anxious at work" or I might say "I want to find reasons not to leave my job" or I might say "I just want to do my job with no problems or issues" or I might say "I want to learn how to approach my team lead with this problem" or possibly (and this is something I've done) "I want to feel better venting to others"

See my comment above, you know him better than me, but if I really wanted it to stop I'd ask politely one day, assuming good intentions (see my top level comment) why he does it.

Something along the lines of: "I've noticed that you've rewritten my code a number of times and got <buddy> to approve it, and I really haven't been able to figure out why."

If so, be prepared, some people can be a bit either on or off I guess.