Games like Starship Guardian
Games like Starship Guardian include Legion TD 2 - Multiplayer Tower Defense, Bloons TD 6, Plants vs. Zombies GOTY Edition, Desktop Defender, and That's not my Neighbor. We matched them by the tags players give Starship Guardian on Steam (Auto Battler, Casual, PvE, Tower Defense, and Indie): closest matches first, and among equally close ones the better-known games.

Legion TD 2 - Multiplayer Tower Defense
Shared: Auto Battler · Tower Defense · PvE

Bloons TD 6
Shared: Tower Defense · Casual · Singleplayer

Plants vs. Zombies GOTY Edition
Shared: Tower Defense · Casual · Singleplayer

Desktop Defender
Shared: Auto Battler · Casual · Tower Defense

That's not my Neighbor
Shared: Casual · Point & Click · Indie

Zero Stress King: Idle Defense
Shared: Auto Battler · Tower Defense · Casual

There Is No Game: Wrong Dimension
Shared: Indie · Point & Click · Casual

MUSYNX
Shared: Casual · Indie · Arcade

Razortron 2000
Shared: Casual · Indie · Arcade

Space Rock Breaker
Shared: Casual · Arcade · Top-Down

Rhythia
Shared: Casual · Point & Click · Arcade

Papers, Please
Shared: Indie · Point & Click · Singleplayer

Creeper World 4
Shared: Tower Defense · 3D · Space

Cyberhunt
Shared: Casual · Indie · Arcade

Gorogoa
Shared: Indie · Casual · Point & Click

Timberman
Shared: Casual · Indie · Arcade

Game Dev Tycoon
Shared: Casual · Indie · Singleplayer

Rogue Tower
Shared: Tower Defense · Casual · 3D

Vampire Survivors
Shared: Indie · Casual · Arcade

Orcs Must Die! 3
Shared: Tower Defense · PvE · 3D

Mountain
Shared: Casual · Indie · Singleplayer

Hidden Folks
Shared: Casual · Indie · Point & Click

AudioSurf
Shared: Casual · Indie · Arcade

Spin Rhythm XD
Shared: Casual · Indie · Arcade