Can I get some 20 dollar s*** off Temu with a coupon and still expect it to work with apple fitness, Technogym and other apps I use for sport ? I’d like to be able to monitor my heart rate at the gym and connect with the equipment for instance but I don’t really deserve any luxury/expensive s***

You can get like a used Garmin or Polar chest strap heart monitor that’s more accurate than a band for like $30

Airpods and a copy of The Smiths' hit record The Queen is Dead

Get a chest strap as suggested above, generally the HR monitors on bands or smart watches are not reliable enough for the gym, since the blood will not flow as regularly through the arm while you're lifting