It seems that they remove this "auto-redirect" option from their widget/gateway creation page. I can't find that option in my end.
I found a guide from youtube but it includes the auto-redirect option look
https://youtu.be/bfvZk_6o0Gc?t=399Why not try to contact mycelium gear support you can use this email:
gear.support@mycelium.comAre you using CMS(Wordpress or drupal) on your website or it's a custom website?
Much better to switch to another payment gateway I suggest you try
BTCpayserveror other payment gateway listed from here
https://github.com/alexk111/awesome-bitcoin-payment-processors