You can add an ::after pseudo-element with a huge flex-grow, so that the flex-grow: 1 of the li elements will be negligible:
ul::after {
content: '';
flex-grow: 1000000000;
}
ul {
display: flex;
flex-wrap: wrap;
list-style: none;
padding: 0;
}
li {
flex-grow: 1;
padding: 20px;
margin: 10px;
background: #ddd;
}
ul::after {
content: '';
flex-grow: 1000000000;
}
<ul>
<li>lorem</li>
<li>ipsum</li>
<li>dolor</li>
<li>sit</li>
<li>amet</li>
<li>consectetur</li>
<li>adipisicing</li>
<li>elit</li>
<li>sed</li>
<li>do</li>
<li>eiusmod</li>
<li>tempor</li>
<li>incididunt</li>
<li>ut</li>
<li>labore</li>
<li>et</li>
<li>dolore</li>
<li>magna</li>
<li>dolore</li>
<li>magna</li>
<li>aliqua</li>
</ul>