2020-06-14 (updated 2020-06-27)
The game that would become Risk was adapted from La Conquête du Monde. Two main adaptations were established. The North American variant is most commonly used as a pattern for videogames, whether it be official, unofficial, or clone games.

An important aspect of the board game is often diplomacy; which the official rules specifically and quite purposefully do not forbid nor enforce. Alliances, betrayals, quid pro quo, are entirely off-the-board. This presents and interesting aspect for a developer creating a digital version. This touches on a broader subject I may post about later.

There is also the European variant where players are given a Secret Mission. Later, many official versions of the game would introduce new elements. The Secret Mission rule would be introduced to the rest of the world. A deck of cards with added rules, Capitols, and Commander Units (also various other units) for some editions. Defense oriented rules for the RisiKo! edition. There was a short lived Castle Risk variant. Some of the themed variants, such as the Lord of the Rings and some Star Wars editions, add minigames.

Returning to the videogame versions; there are categories of Risk games:
An official translation based on an official board game variant. These tend to favour the original Risk board game rules.
An official Risk themed game. Divergent from any official board game variant. Ultimate Risk, Risk II, and RISK: Factions, for examples, are original games that have much less in common with the board games (note: these are usually bundled with versions of the original but the main game is divergent)
Straight Clones, that loosely or precialy use the rules of an official board game edition of Risk. Usually the original board game.
Clones, that borrow many aspects of the original either directly or through their own board game clones. Defender of the Crown. Axis & Allies. Settlers of Catan. Lords of Conquest. Annals of Rome. Medieval Lords.

Risk
Risk-Theme
URisk
/Risk-Unlicensed/Risk-Unl
Risk-Like

2020-06-27
I definitely would go for risk-like for all the games borrowing game-play aspect ( the actual risk tag )
And then using risk for the official games.
I'm not sure about the straight-clones category, it sounds too much like the risk-like.
The risk-themed should be an additional tag to add to games already having the official risk tag ?