Welcome back! “New Player” is a very low traffic forum, so chances are you won’t find many people from your own realm on here. But I wanted to touch on a couple things for you and give you a couple links of where you may be able to find yourself a guild that will suit your needs.
First things first, over the years some servers have been merged with other ones. Burning Blade is one such server. So when you are sitting in Orgrimmar for example, you may notice people from other realms (what used to be individual servers are now called “realms”, and the collection of realms make up the server). Specifically, you will see people from Burning Blade, Lightning’s Blade, Onyxia, Garona, Icecrown, and Malygos.
All people from these realms are essentially on the same server. You can play together with them as if they were all on Burning Blade. It would take a lengthy post to really deep dive into it, but for the purposes of your question this also means you can join a guild on any one of these realms, which will open up a lot more options for you in your search. Here are a few places I would recommend looking:
New player friendly guilds sticky thread:
There are a lot of guilds posted here that love to help out new and returning players, but they are from an array of different realms, so you will have to search the thread for any that may be on the realms that I listed above.
Realm forums:
https://us.forums.blizzard.com/en/wow/c/burning-blade-lightnings-blade-and-onyxia/121 (Burning Blade, Lightning’s Blade, and Onyxia)
https://us.forums.blizzard.com/en/wow/c/garona/68 (Garona)
https://us.forums.blizzard.com/en/wow/c/icecrown-and-malygos/156 (Icecrown and Malygos)
Blizzard hasn’t done a very good job at combining the individual realm forums, so they are spread out in 3 places.
Trade chat! /2 is still a good way to find guilds, but not nearly as many tend to post in it anymore. Drop a line in there that you’re looking for a friendly guild to help a returning player and you might get a few hits.
The in game guild finder tool: This was revamped a couple expansions ago, and is actually really useful now. Search the “social and leveling” guilds section and apply to any that sound like they might be what you’re looking for. Check back often to see if your application has been accepted.
Don’t be afraid to guild hop until you find something that feels like it would be a good home for you. There are a lot of guilds out there with a lot of different focuses.
As far as this is concerned, when the Shadowlands expansion launched, there was a level squish. Everyone who was previously level 120, was taken back down to level 50. Level 60 is once again max level. Until next expansion anyway. 
I wish you the best in your search, and again, welcome back to Azeroth!