Since Zoom does some post-processing of your audio input, it's best to hear yourself in a Zoom recording:
Right-Click on the speaker icon in your tray, then go to Sound Preferences => Input.
On a notebook you want to get sound from your microphone jack and not from the internal microphone.
A desktop PC will often have multiple microphone jacks (front microphone, rear microphone).
Make sure the right microphone jack is selected in the Linux input settings.
The Linux input settings also have a live meter showing you the volume of your input feed.
Talk into the microphone and watch the meter.
In the Zoom settings, go to the Audio tab.
Under Select Mic you should select "Build-In Audio Analog Stereo", or the name of an external soundcard if you're using one.
The Zoom audio settings also have a live meter showing you the volume of your input feed.
Talk into the microphone and watch the meter. The meter should move as described above.
Try unchecking "Automatically adjust volume" and setting an input level manually.
Prefer controlling the input level over the Linux input settings, and not Zoom, so amplifications happens as close to the source as possible. This might mean selecting the lowest possible input level in Zoom.
Again check how the meter moves as you talk into your microphone.
If you hear cheeping or other electronic noise in your recording, make sure the microphone cable doesn't cross any other cables, especially power cables.
Internal cards on desktop PCs are often cheap components with bad shielding. If problems persist, try using a different microphone jack. This will not help if the internal soundcard uses unshielded wiring inside your desktop tower.
If issues persist, try using an external soundcard. We have some USB sound cards that look like USB thumb drives with headset jacks.
You may also try an headset with an USB jack (instead of an analog 3.5 mm jack), which have their own sound card.
An USB sound card should be detected by Linux automatically. After plugging it in you need to select it in:
The native Zoom application itself or how it interacts with your setup could be the problem. As a last resort you could use Zoom with your Chrome Browser and test if problems still persist.
Caveat: You won't be able to use all the native Zoom features (e.g. to blur your background).