Good evening everyone.
My name is John and I write from northern Italy, a small town near Venice.
I wanted to ask this community if there is a lets encypt multi-domain primary certificate that can support approximately 50 domains in Windows hosting, preferably with a maximum of 3 subdomains for each primary domain, and possibly how to obtain it.
I don't know what you mean by a "primary" certificate, but Let's Encrypt certificates can contain a maximum of 100 hostnames. So yes, 50 should be fine, even if you include the www subdomain for every domain name. (50 * 2 = 100, so a maximum of 50 domains if all domains include the 'bare' apex domain and the www subdomain.)
I have no experience with Windows in this matter, but there are a few ACME clients specifically designed for Windows, see e.g. ACME Client Implementations - Let's Encrypt for a (probably non-exhaustive) list of those. Some are easily set up, some are more difficult. Some are completely open source and by "the community", others are backed by a commercial company.
You have deleted the mandatory questionnaire which was presented to you in the Help section, so we cannot give you any specific hints or tips besides these generic advices.
Sorry for inconvenience, I didn't notice the questionnaire.
I don't have good experience of English I'll try to look it up and compile it thanks for the reply.