Hi @haryadihart
In addition to @Fubar response. One step deep dive into where you can adjust column settings
In portal management:
1. Under content> Lists> Choose your list
2. Options > Enable "Advanced settings" checkbox
3. Under the "Override Column attributes" > Change the size of the column

4. Note: By default value entered in step 3 is percentage. If you want to be in pixel. change the Grid config to Pixel like below

Output:

After overriding column attributes :

If you want the user to change the column width according to their customisation, Javascript is the way.
Hope it helps.
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