Need info on how to find websites for backlink building

Hello guys, I have been doing backlink building for a few months now. I have been doing good so far but the problem I have now is that: I have a list of websites (I literally found it on a fb group and it has over 200 websites on it) that are indexable and they are good but I would like to learn how to find those websites on my own. What should I look for? How do I know if a website is indexable? I need forums and edu sites that can be indexed with my backlinks that are from the area of Germany or Austria. Any help will do!

Link building takes ingenuity. There are hundreds and hundreds of threads on this forum that will tell you exactly how to find sites in your niche that MAY accept guest posts or be suitable for link building. Use the search function.

1 part method search forums in Google use operator AND or other:
forum AND keyword
Search link to your competitors and then check theirs sites by Ahrefs tool

2. part Competitor analysis
- form a list of your competitors
- Log in to ahrefs.com and then switch to Backlinks section
- select forums and edu sites from profile.

Don't ask questions like this anymore. You have there like 3-4 questions and it all looks like they're the same question tbh. It's better if you do it like this 1)question, 2)question 2...

To answer your questions

1) To find backlink opportunities, the best bet is Ahrefs (7-day trial and you can export their backlink profiles. Make sure you check their Youtube Channel if you want to get handy with it)
2)I don't believe that any list that is shared publicly has a lot of value tbh. I don't have that exact list, but I can say that I'm correct for 90% of the lists that there are shared. I guess they're mostly profile, blog comments backlinks which in today era are almost useless.
3)Since you mentioned that your focus is in Austria/Germany, you should also know that in foreign SEO you can get way easier with algo than with US version (.com). Also, keep in mind that even .com links do wonders for foreign markets.

Go to ahrefs and check competitors backlinks and download do follow backlinks and make on it