I struggled with this same problem for a long time before finding a solution. I really didn’t want to give up and run my reverse proxy (Traefik in my case) on the host, because then I’d lose out on all the automatic container discovery and routing. But I really needed true client IPs to get passed through for downstream service consumption.
So what I ended up doing was installing only HAProxy on the host, configuring it to proxy all traffic to my containerized reverse proxy via Proxy Protocol (which includes original client IPs!) instead of HTTPS. Then I configured my reverse proxy to expect (and trust) Proxy Protocol traffic from the host. This allows the reverse proxy to receive original client IPs while still terminating HTTPS. And then it can pass everything to downstream containerized services as needed.
I tried several of the other options mentioned in this thread and never got them working. Proxy Protocol was the only thing that ever did. The main downside is there is another moving part (HAProxy) added to the mix, and it does need to be on the host. But in my case, that’s a small price to pay for working client IPs.