Grenades and other capsules can be thrown again in Factorio 2.1.19, according to Wube's September 16 release notes. The correction is available through the experimental branch.

The failure affected version 2.1.18

Wube acknowledged the issue in the linked 2.1.18 bug report and released 2.1.19 later that day. The newer version's changelog lists the throwing fix as its only change.

Official Factorio screenshot showing turrets defending a walled factory against enemies.
Official Factorio combat screenshot. Wube’s 2.1.19 note addresses grenade and capsule throwing; this image illustrates the game and is not a patch test.Wube Software

Update through the experimental branch

As of September 20, Wube still lists 2.1.19 as the experimental download.

The stable version remains 2.0.77. This hotfix does not mark the 2.1 series' promotion to stable.

For Steam, Wube directs players to the experimental option under Beta Participation in the game's settings. Standalone players can enable Experimental updates under Other settings.

If the throwing failure interrupted a session on 2.1.18, check the installed version and update to the corrected build before trying grenades or capsules again.