I was able to successfully setup a dedicated server using my backup PC and it works well. I had to go into my Xfinity App to setup the port forwarding to that specific PC, so you should have to do something similar I would imagine with your ISP. Also, if you have any other things running on the computer, check those too like Anti-Virus or Windows Defender.

I used this guide mainly: https://www.pcgamer.com/valheim-multiplayer-dedicated-server/

Also, I used this post to troubleshoot some things as needed: https://steamcommunity.com/app/892970/discussions/0/3103515720272633154/

Let me know what is going on and where you are having issue and hopefully I can help you out since I just did this over the last few days. The best thing about getting this way to work is that it's not costing me any monthly fee, so don't give up!

I haven't tried renting a Valheim server yet, but I've rented and administrated servers for Ark, Space Engineers, etc. a bunch of times.

Nitrado: Probably the best ease of use and UI of any of the hosting companies I've tried. It's too bad that their performance is so terrible. Not only will you see more lag than with competing hosts but you'll experience more server outages as well. I would avoid this one.

Serverblend: Kind of hit or miss depending on the game. The UI is the worst I've ever seen, but customer support is pretty decent. If you like their vibe they're worth a try.

G Portal: Good UI, good performance, and fantastic customer service. I had a great time with this host right up until our server got corrupted and they lost all our data. There's no way to schedule regular backups so going with this host is a gamble for sure.

GTX Gaming: Nothing about GTX stands out as great except for the fact that there are no downsides that I can tell. The performance isn't fantastic but it's better than Nitrado, and the UI is garbage but at least it's not Serverblend. This is the one I would recommend today.

All of them are similarly priced with most server packages running around $15/month