Changing the default keysize in Webmin does not affect any existing SSL certificates. You’d need to re-generate those SSL certificates.
I haven’t tried using 4096 bit keys for Let’s Encrypt previously, but I suspect it’d work. A quick Google search suggests that Let’s Encrypt does support it, so that should work just fine.
That said, certainly try a test on one after making that change to see if it works as expected.
The try, ok i understand.
That LE is / should working ( other CP) with 4096 i know)
I remember only that i tried before with setting up last year the box the 4096 i get errors, but probably i did thing the wrong way, and started a fresh install then.
Left the 2048 on the VM Box
Later in Summer maybe i give it a try, is a produktion box for at least 1 Website for winter. ( i don’t want to break… if doing parts not right)