I sometimes listen to deathcore/etc. metal too and honestly, just like with any other genre, your open back headphones shouldn't really be leaking that much sound if you're listening at normal hearing levels.

If you're playing games with repetitive particles or special effects, it might get annoying if other people are in the same room as you and they have like sensitive hearing or something.

For the most part, it shouldn't be that loud, you'll know what I mean as you can just leave the headphones on the table after setting your comfortable volume and then that's basically what other people kinda hear around you when you're wearing it.

Open back headphones and solutions to PC noises: https://www.reddit.com/r/headphones/comments/11dh2v9/is_there_anything_i_can_do_stop_hearing_my_own/ja8mltw/ and https://www.reddit.com/r/HeadphoneAdvice/comments/xpa9zd/pc_noise_with_open_back_headphones/iq2znjn/

Use parametric EQ for metal/etc. or look at this thread on Head-Fi: https://www.head-fi.org/threads/iem-for-metal-music-and-hard-rock-ultimate-solution.885104/page-122

Make sure that you have a vacuum seal with the ear tips for IEMs/TWS earbuds, and then for headphones it's the earpads. This will help with the noise reduction/isolation and should prevent you from getting tempted to raise the volume against the external noises in order to hear your own music/sounds.

Click this sentence for more info on the importance of ear tips sizing, dimensions, et cetera.

Click this sentence for comfort and everything with ear tips.

Click this sentence for how to put ear tips on wide nozzles (basically aim it at different angles and force it, be careful not to overdo it as it can damage the core/stem/stalk/etc. of the ear tips).

This is how you should use Etymotics or really any IEM or TWS earbud to make sure you have that good/perfect fit for that vacuum seal (necessary for the bass to be properly produced): https://www.youtube.com/watch?v=8KwXEqe6Gq4

Here's a bit more info on IEMs, hearing health, earwax cleaning, parametric EQ to compensate, et cetera: https://www.reddit.com/r/headphones/comments/11nwy92/uneven_headphones/jbplupa/

Info about measuring decibels, hearing health, et cetera here: https://www.reddit.com/r/headphones/comments/11a4cpm/are_few_second_peaks_into_8285_db_still_safe_when/j9riw7q/