Well, for sure, i-MSCP was a good solution, and finding something similar is hard 😁
KeyHelp could have been a way to go (where an old user of this panel made a migration script to move on it), but the code is obfuscated/crypted ==> It's a "No Go" (if one day, they make it as a "pay solution", you'll be stuck with it and will suffer a lot).
In the end, I chose to go with ISPConfig (which have Let's Encrypt, and also DNSSEC support).
The "bad counterpart" with it is that all the stuff is mostly manual (you can define a template for the DNS, but that's all).
Creating a web site, where i-MSCP create the DNS, default mail accounts, etc... aren't made with ISPConfig, every section need to be done manually.
Some good points though : Emails account are easily "migrable" as you can keep the salted password from i-MSCP to this new system (moving over 125 mails accounts (+ approx. 200 forward accounts), with the data migration, had been made in 2-3 hours).
There might be other solutions available, but it was a long old time plan to move to ISPConfig (2012 😂 but then, i-MSCP did rise, and this initial plan was gone).
Good luck in finding the one that fit your need 😉