IMO Team Viewer was a rip off when the licence cost was a once only fee, more so now that they want the same amount annually.
I use remote desktop with a port forward (using a non standard port e.g. 50123 mapped to 3389) from the outside world and some security settings that lockout login for 30 minutes after 3 unsuccessful attempts. There is a nice RDP app available for iPad.
If Remote Desktop is not an option then Anydesk is a good alternative, free for personal use.
www.anydesk.com