Lethal_Entity

Defeating gyms unlocks the legendary map pokemon from that region, here's the list of regions and the released legendary map pokemon belonging to each :
 
Kanto - Articuno , Zapdos , Moltres , Mewtwo Johto - Raikou , Entei , Suicune , Lugia , Ho-oh Hoenn - Regirock , Regice , Registeel , Latias , Latios , Kyogre , Groudon , Rayquaza  Sinnoh - Uxie , Mesprit , Azelf , Dialga , Palkia , Heatran , Regigigas , Giratina , Cresselia , Arceus (in PV). Unova - Cobalion , Terrakion , Virizion , Tornadus , Thundurus , Reshiram , Zekrom , Landorus , Kyurem. Kalos - Xerneas , Yveltal , Zygarde (map legendary form, you dont need gym badges to unlock zygarde cell.....I think). Alola - Type-Null --> Silvally , Tapu Koko , Tapu Bulu , Tapu Lele , Tapu Fini , Necrozma. Galar - Zacian , Zamazenta , Eternatus , Kubfu. To be able to catch event pokemon which can be caught during an event........I believe you need to complete all the gyms.

Yes there is an option called "available to chat" which if you toggle off, you cant see that person's chat tab in the list.

Also I already answered this to you through mail like 5 minutes ago 😅

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Go to your profile Just above reputation you will see your profile pic, yours is a "D'' at the moment, on the lower left side of the circle which contains your profile pic there is an option called "profile photo" enclosed in a small square. Click on that and a pop-up will open on your screen with two options "Upload photo" or "Remove photo", choose "remove photo" if you want to change your profile pic back to default (the "D" you have right now is your default profile pic). Select "Upload photo" and just select the pic or gif you want as your pfp.

              For reference : https://imgur.com/a/nO2Uw00

 

I'll link you to the posts which contain the training accounts since there are 3+ different accounts for different types of pokemon: 
I dont use the accounts listed in the former post by patrick which are for training non immune pokemon since different and better accounts have been made for certain types (imo), so other available accounts are listed in the latter post in case you prefer one account over the other.