Cannot SSH to LE 11.0.1 on new RPi4

Hello, just installed LE 11.0.1 on new RPi4. Wrote the uSD card with Raspberry Pi Imager. Install went very smoothly, but now stuck on a few details.

I did all the install with direct connect Keyboard Mouse Video, but intend to run "headless", so want to get SSH working. I enabled SSH and Samba on the initial install. I've been using Putty on my RPi2 WiFi (LE 9.2.8) without any problems, and continues to work. But on the RPi4 (WiFi), Putty session won't even start, get the error "couldn't agree on a key exchange algorithm....". So, no login prompt presented.

Probably not pertinent, but thrashing about, I found same result regardless value of Settings>LE>Services> Disable SSH Password= Off (i.e. disabled) or =On (i.e. disabled).

Strangely, I was using Putty v 0.64 and got this key exchange error many times, so upgraded to Putty v 0.79 and got a different error msg the first time I attempted Putty v0.79 session...The first time got to login prompt, I entered "root", then immediately received "no supported authentication methods available". Second and subsequent attempts give the "couldn't agree on key exchange algorithm error. "

SSH public private keys are a mystery to me, probably fairly obvious Please help.

Hi Chewitt, I used regedit to delete Putty's SSH keys for RPi4 IP address XXX.YYY.0.86. Also assured LE password disable is off with Settings>LE>Services> Disable SSH Password= Off (i.e. passwords required).

At this point, I realized I had two versions of Putty floating around v 0.64 in Program Files(x86) and v 0.79 in Program Files. Carefully choosing v 0.79, SSH sessions behave correctly. Thanks for you help!

BTW, I'm confused on the meaning of Settings>LE>Services> Disable SSH Password= Off I would assume this would be the easiest but least secure setting...but for some reason password must be enabled....not a problem, but don't understand why?