how to test ios and watch os betas

my suggestion is: wait for awhile

when the public beta is coming.
sometime on july.
right now, it can be a lots of buggy and crashes

If you haven't already done so, You can read about the Apple Beta Software Program here and also sign up: https://beta.apple.com/sp/betaprogram

Once the iOS 16 beta becomes available to public beta testers, you go to beta.apple.com on your phone. This will let you enter your Apple ID into the beta program and let you download the "Configuration Profile" to your phone.

Once the profile is installed, you'll get the betas through the software update option in settings just like any other updates, and if you ever want to leave the program you delete the profile from your phone also in the settings. Just keep in mind that deleting the profile won't downgrade you to the current stable iOS release, it'll just make you stop getting new betas. If you decide you want to return to iOS 15 during the beta cycle, you need to connect your phone to a computer and run a restore with iTunes on Windows or Finder on Mac.

The procedure for the watch is nearly identical, you get the watch beta profile through your phone on the same page and you'll start seeing betas in your watch's software update. The one major difference here is that there's no way to downgrade a watch to a previous Watch OS version, so if something on the betas would really give you trouble the only way to get it downgreaded is sending it to Apple.

If you're scared at all, it's not the right path to take. In most cases you're going to be absolutely fine, but never run beta software on a device you can't afford not to be using. If you want to experiment, get hold of an old iPhone for test purposes, and remember to do a backup through Finder or iMazing beforehand so you can revert if things aren't to your liking.

Beta software is beta software for a reason. If you feel comfortable taking the risk, do so, but if you aren't comfortable with a potential screwup and you can't live without the device in question, don't.

Testing is very risky on iOS and Mac. It is very risky. My friend is currently testing out iOS, and he says that his phone is currently not working at all, no matter what he does. Not for me, though, because my phone is working completely fine. That being said, you should not under any conditions test iOS on your primary devices. So if I were you, make sure that you have a secondary phone or Mac to test with, and do not run on your current device you own..

I have had no issues with public beta's however only you can decide if you want to take the risk.

I have had no issues with developer betas of ios. Unfortunately, I cannot run MacOS Ventura ‘cause its not supported. It’s an early 2015 MacBookPro and I think the cutoff is that. As far as I am aware, the newest Mac, that is supported by Ventura beta, is 2016. Please correct me if I am wrong on this matter. I hope I am!

I don't have an Apple watch, so someone chime in. i think the series four isn't getting watch OS nine. again, don't quote me. I run the betas on Mac and so far, i'm ok. You don't sound like a person who takes risks much, which is completely your decision. I'd just be extra careful. It's like that with any IOS release, once the new version, people usually can't downgrade after about a day so some just don't even update.

Applewatch series 4 will get watch os 9 no problem. Per the article on google,
watchOS 9 will be available this fall as a free software update for Apple Watch Series 4 or later paired with iPhone 8 or later and iPhone SE (second generation) or later, running iOS 16. Some features may not be available in all regions or all languages, or on all devices. Features are subject to change.
Anything before watch series 4 is getting dropped and will not get the update, series 3 and below.
watchOS 9 has officially dropped support for the Apple Watch Series 3, as it will only be compatible with the Apple Watch Series 4 and later.

I will wait for it released in the end of september or early October.
I am using IPhone 12 but, don't have too much confident to test it yet.

I have thought of running a beta test on my iPad Pro six generation, but I probably shouldn’t because most of my other apps that I use are on it and not on my phone. My phone is mainly just as a telephone, a music player, a web browser when I’m on the go, a way to communicate with my School friends and family, so that puts beta testing on it completely out of the question.

1. Never run betas on your primary devices. You don't want to be lost in a public area needing help, and unable to call someone because your phone decided to get into a crash loopp for no reason.
2. You cannot uninstall betas on Watches. So once you have WatchOs 9 beta on your watch, thats it. If you don't like it, or it gets into a bootloop, your only option is to get it serviced by apple.