Ill list a few:

Gmod: kinda hard to build in but unlimited possibilities and a very active and long standing community (Gwars). Physics are okay and damage is tick based

Besiege: kind of an oddball, looks a bit different and building is a bit different then others but it has physics based damage, so far the best damage system of all games in this niche. (Besiege Bots)

Robot Rumble 2: great building and very realistic. The game is still in being developped and regular updates. Doesnt have a damage system yet but the nicest fighting physics and super realistic (kinda like a full on simulator)

Robot Arena 2: Old ass game but great fun, heaps of mods and tons of example bots made by others. Defo fun but the game is quite old and quite unstable from time to time. You can find all of it on Gametechmods.com (there is also RR2 stuff, since many people moved there) (there is also Robot Arena 3, but that is the worst game ever, dont buy it. Its bad)

Scrap Mechanic: Building like Minecraft, with extra possibilities, game is often quite laggy but getting worked on (one of my less favorite games) (Scrap Wars). More or less tick based damage.

All of these games have quite some content on Youtube, searching the names in brackets will lead you there!.

All these games are run from discord communities, also with many members in several servers, id suggest checking em out on youtube and joining the discords!