How to index backlinks and other's webpages in Google?

You must use Indexing services.

I’ve found that getting links indexed is like herding cats these days, but having your backlinks on sites with actual feet on the ground helps a ton. I usually double-check for 'noindex' before bothering with submission tools, saves me some hair-pulling. If Google Search Console takes forever, I just focus more on amping up the link quality instead of chasing every indexer out there.

indexing is not guaranteed anymore but google decides what it wants to pick up. best approach is to make sure the linking age itself is crawlable and has some quality signals. internal links + natural crawling usually work better than forcing it with tools.