I'm not entirely sure what you are saying, goliath and taxabi are not in the player handbook, they are in Volo's guide. The default option given on the sheet are those that are free and mentioned in the Basic Rules, if you look at the classes and spells, you see much missing also. You should be able to modify your race to something not in the menu, but then you probably manually have to add what bonuses it gives and what not. If you or your DM have bought the books in roll20, you have access to them in the compendium. What comes to how "legal" a race, class or spell is, depends on the DM. Generally there could be said to exist 4 levels of "legality" for 5E, starting from the strictest: 1.Adventure League(AL) legal only. Shortly it means PH + one other book is okay when you create you character. No race with flight at 1st lvl. Used in officially run campaigns. 2. Any official books legal. Most common, 5E don't have so many books yet. 3. Unearthed Arcana(UA) might be legal. UA are a bunch of races, classes and spells that are unofficial but released as test-things by the official developer. Some UA stuff have later been added to newer books after some rework. Are considered a bit unbalanced, but still way better than homebrew. 4. Homebrew might be legal. Very few DMs allows homebrew, because it can be very unbalanced, these this are always needed to run through the DM even if they allow them. Most GMs are either 1 or 2, but whatever their restrictions are, they often state what's allowed and what's not. If you what be extremly sure that you have a "legal" character concept ready for a game on short notice, make a AL legal version character you can fall back to. There might even be DMs that only allows the stuff in the PH or only the free rules. As always, ask the DM if he/she isn't clear about this. Edit: So even by the strictests rules, Goliath and Taxabi are considered legal.
