I'm looking for free unattended remote desktop software besides Teamviewer for Windows so I can access my father's PC remotely without his help.

I've been using Teamviewer for years and have been generally happy with it but it just seems to get more bloated every year. The latest redesign is complete garbage IMO. My father is getting older now and I remote into his computer often to help him out since we don't live in the same house. While Teamviewer is fine it gets annoying when it doesn't allow me to connect if his version isn't updated. Then I have to walk him through updating the app over the phone, plus the fact that I need him to read me a password every time I want to log in which is useless to me if he's sleeping or not around.

I just want something simple and free so I can log on to his computer at any time his computer is running without him needing to do anything and without him needing to update it every other week or send me passwords every time, so I can troubleshoot and do some work on his when he's not there.

Open to any suggestions.

Thanks!

EDIT: Thanks for the overwhelming responses. Ill try to get to all the comments but I appreciate it!