Right now I’d say the best open-source DAW for Linux is LMMS if you want to do everything just on your laptop, or Ardour if you want to use external instruments.
LMMS has some shockingly versatile built in synths, including a port of ZynAddSubFX, supports LADSPA/LV2 plugins, and supports using Wine to run 32-bit Windows VSTs. I’m unsure of Ardour’s VST support, but it at least supports LV2 plugins. Either of those, if you install them through your distro, will likely include Calf Studio Gear, an extensive collection of LV2 effects and a couple synths. As for ones that run natively on Linux, there’s synthv1, samplv1, drumkv1, and padthv1, though I’ve had trouble getting them working myself.
I’ve found some good stuff on the Linux Audio Wiki but IDK how up to date most of it is.