Seeing it on your PC
Most of what your PC sends goes to port 443: browsers, Windows Update, Office, OneDrive, Teams, games and almost every app. Malware uses it too, because it blends in.
Should you block it?
You cannot judge a 443 connection by its port. Look at which program made it and who owns the address. Nothing should listen on 443 unless you run a web server.
Check it on your PC
Run this in PowerShell to see what is using port 443 right now, and which program owns it:
Get-NetTCPConnection -LocalPort 443 -ErrorAction SilentlyContinue | Select-Object LocalAddress,LocalPort,RemoteAddress,RemotePort,State,@{n='Process';e={(Get-Process -Id $_.OwningProcess -ErrorAction SilentlyContinue).ProcessName}}Get-NetUDPEndpoint -LocalPort 443 -ErrorAction SilentlyContinue | Select-Object LocalAddress,LocalPort,@{n='Process';e={(Get-Process -Id $_.OwningProcess -ErrorAction SilentlyContinue).ProcessName}}No output means nothing is using the port at the moment. For every connection at once, paste netstat -ano into the netstat explainer.
Block it in Windows Firewall
In PowerShell run as administrator, this stops other computers from connecting to this port on your PC. It does not stop your own programs connecting out.
New-NetFirewallRule -DisplayName "Block inbound TCP 443" -Direction Inbound -Protocol TCP -LocalPort 443 -Action Block
New-NetFirewallRule -DisplayName "Block inbound UDP 443" -Direction Inbound -Protocol UDP -LocalPort 443 -Action Block
Undo it with Remove-NetFirewallRule -DisplayName "Block inbound …", using the same name. If you depend on the service on your local network, this rule stops that too.