In the past i made some codepens for this issue (Very usefull trick/idea).
1. Video.JS - autoplay + sound
Her I have an example of embed video (Remodal + Video js) and modal (Works fine/smooth). Less than 5 min to move this codepen to webflow (If you want i create for you step by step example)
2. youtube example - autoplay + mute
Clever code with youtube API - but no way to autoplay (Only work when mute: 1,) - There is no way around this (Google it)