Thank you for this comprehensive response.
I know how to set up WLM 2012 once I have got it installed on the Windows 10 laptop. All I need to do is copy all the settings (for all the email accounts) I already have on WLM on my Windows 7 laptop.
My concern was that because WLM 2012 wasn't intended for Windows 10, I might run into the kind of issues described in the post mentioned by both you & Don (362021-windows 10 update messed up 2012 WLEssentials Live Mail), especially when Windows 10 automatically does System Updates. If those kind of issues (as in that post) arose I would be totally stressed & I wouldn't be able to sort it out (or would be too frightened to try) and would be worse off (overall) than I am at present.
The uTube video describing how to install WLM 2012 on Windows 11 is very helpful. However he (the man in video) says it includes a link for the download file & I can't see one. Nevertheless the one you quoted should work in the same way I imagine (or may even be the one he intended to include).
Fyi: AOL now requires one to use an App generated password with WLM
Gmail needs one to "Allow less secure Apps" (in gmail account settings) to use WLM
On gmail my smtp server port is 465 (Use SSL checked)
Gmail using POP isn't happy with the same email account on two separate laptops. My view is that it is better to Uncheck "Include this account when receiving mail or synchronising" on one laptop (keeping it checked on the other), then copy any emails one wishes to retain from the actively-synchronising laptop onto a flash drive and then from the flash drive to the inactively-synchronising laptop. There is an alternative but I would find this an easier option as both my laptops are in the same location.
Btinternet is UK based & very common here:-
Server: Incoming mail server (POP3) mail.btinternet.com Outgoing mail server smtp.btinternet.com Check "Log on using clear text". Check "Outgoing server. My server requires authentication" and use settings Log on using account name (one's email account name), Password (one's email account password), Uncheck log on using secure password authentication.
Outgoing mail port 25 (uncheck server requires SSL) works for me but there are other options. Incoming mail port 110 (uncheck server requires SSL) works for me but there are other options
As far as I am aware it is not possible to use Encryption: STARTTLS in WLM 2012 - at least not with POP anyway: the option simply isn't offered.
I am in the UK