Welcome to the forum! This place is super friendly and people are really helpful here so you've definitely come to the right place! As for the plastic toy you mentioned, a good rule of thumb for adding decor into your fish tank is the pantyhose test. Take a pair of pantyhose, if it snags them, then it has the possibility to snag your betta's fins! Also, be sure to check the inside edges on any ornaments or hides. I learned that lesson the hard way with one of my past bettas as I didn't realize that there was a sharp edge inside of his favorite place to hide! I was able to file it down, but you can also cover sharp edges with aquarium sealant/silicone.
Once again, welcome! :)
<3 SIP King & Sir Arthur <3