I don't support this horniness because come on, but...
Have you tried blocking the following using uBlock Origin?
instagram.com##.RnEpo
instagram.com##body:style(overflow: auto !important)
instagram.com##body[style="overflow: hidden;"] .XQXOT:style(width: calc(100% - 12px) !important; padding-right: 0 !important;)
If that doesn't work, just either use the Hide button in uBlock to hide the login pop-up & overlay (this worked for me just now when I tested it incognito in Firefox) or just enable the AdGuard Annoyances & uBlock Annoyances filter lists, which should also work. Disabling JS works for most login pop-ups too on other sites, but I'm not re-opening an incognito window and going to someone's instagram page to see if disabling JS breaks anything else site-wise - probably will though!
they could be though i see your vision comrade