How to submit matrix and category fields in frontend - twig

Question

So i have an entry to submit games.
The games entry has a lot of different fields, and one of the fields is:
a field with fieldType "category" linked to a category
a field with fieldType "matrix" called materialList that looks like this:
The "MaterialName" has fieldType categories and is linked to a category
So now I am trying to submit a form in my frontend.
So far I managed to correctly save regular text fields, but I failed to correctly save something as a matrix, and I failed to properly save a category that is correctly linked.
I already found an example on https://craftcms.com/knowledge-base/entry-form but this only shows me the regular text fields.
This is the code I have so far:
<form method="post" accept-charset="UTF-8">
{{ csrfInput() }}
{{ actionInput('entries/save-entry') }}
{{ redirectInput('spelen/{slug}') }}
{{ hiddenInput('sectionId', '1') }}
{{ hiddenInput('enabled', '1') }}
<label for="title">Title</label>
{{ input('text', 'title', entry.title, {
id: 'title',
}) }}
{{ _self.errorList(entry.getErrors('title')) }}
<label for="youngestAge">Minimum leeftijd</label>
{{ tag('input', {
id: 'youngestAge',
type: 'number',
name: 'fields[youngestAge]',
text: entry.youngestAge,
}) }}
{{ _self.errorList(entry.getErrors('youngestAge')) }}
<label for="oldestAge">Maximum leeftijd</label>
{{ tag('input', {
id: 'oldestAge',
type: 'number',
name: 'fields[oldestAge]',
text: entry.oldestAge,
}) }}
{{ _self.errorList(entry.getErrors('oldestAge')) }}
<label for="leastAmountOfPlayers">Minimum aantal spelers</label>
{{ tag('input', {
id: 'leastAmountOfPlayers',
type: 'number',
name: 'fields[leastAmountOfPlayers]',
text: entry.leastAmountOfPlayers,
}) }}
{{ _self.errorList(entry.getErrors('leastAmountOfPlayers')) }}
<label for="mostAmountOfPlayers">Maximum aantal spelers</label>
{{ tag('input', {
id: 'mostAmountOfPlayers',
type: 'number',
name: 'fields[mostAmountOfPlayers]',
text: entry.mostAmountOfPlayers,
}) }}
{{ _self.errorList(entry.getErrors('mostAmountOfPlayers')) }}
<label for="groups">Aantal groepen</label>
{{ tag('input', {
id: 'groups',
type: 'number',
name: 'fields[groups]',
text: entry.groups,
}) }}
{{ _self.errorList(entry.getErrors('groups')) }}
<label for="gametime">Speelduur</label>
{{ tag('input', {
id: 'gametime',
type: 'time',
name: 'fields[gametime]',
text: entry.gametime,
}) }}
{{ _self.errorList(entry.getErrors('gametime')) }}
<label for="intro">Intro</label>
{{ tag('input', {
id: 'intro',
type: 'text',
name: 'fields[intro]',
text: entry.intro,
}) }}
{{ _self.errorList(entry.getErrors('intro')) }}
<label for="purpose">Doel van het spel</label>
{{ tag('input', {
id: 'purpose',
type: 'text',
name: 'fields[purpose]',
text: entry.purpose,
}) }}
{{ _self.errorList(entry.getErrors('purpose')) }}
<label for="explenation">Speluitleg</label>
{{ tag('input', {
id: 'explenation',
type: 'text',
name: 'fields[explenation]',
text: entry.explenation,
}) }}
{{ _self.errorList(entry.getErrors('explenation')) }}
<label for="gameType">Spel type</label>
{{ tag('input', {
id: 'gameType',
type: 'text',
name: 'fields[gameType]',
value: 6,
}) }}
{{ _self.errorList(entry.getErrors('gameType')) }}
<label for="materialItem">Material</label>
{{ tag('input', {
id: 'gameType',
type: 'text',
name: 'fields[materialItem]',
value: entry.materialItem,
}) }}
{{ _self.errorList(entry.getErrors('materialItem')) }}
<label for="isPublic">Publiek</label>
{{ tag('input', {
id: 'isPublic',
type: 'checkbox',
name: 'fields[isPublic]',
text: false,
}) }}
{{ _self.errorList(entry.getErrors('isPublic')) }}
<label for="body">Body</label>
{{ tag('textarea', {
id: 'body',
name: 'fields[body]',
text: 'test bericht',
}) }}
{{ _self.errorList(entry.getErrors('body')) }}
<button type="submit">Publish</button>
</form>
So these are the 2 I need help with:
The first input needs to properly save linked categories
The second one needs to properly save a matrix
<label for="gameType">Spel type</label>
{{ tag('input', {
id: 'gameType',
type: 'text',
name: 'fields[gameType]',
value: 6,
}) }}
{{ _self.errorList(entry.getErrors('gameType')) }}
<label for="materialItem">Material</label>
{{ tag('input', {
id: 'gameType',
type: 'text',
name: 'fields[materialItem]',
value: entry.materialItem,
}) }}
{{ _self.errorList(entry.getErrors('materialItem')) }}

Answer 1

So I found out how to save a category, but I'm still stuck on the matrix part.
This is the code for the category:
{# Include a hidden input first so Craft knows to update the existing value
if no checkboxes are checked. #}
{{ hiddenInput('fields[myFieldHandle]', '') }}
{# Get all of the possible category options #}
{% set possibleCategories = craft.categories()
.group('food')
.all() %}
{# Get the currently related category IDs #}
{% set relatedCategoryIds = entry is defined
? entry.myFieldHandle.ids()
: [] %}
<ul>
{% nav possibleCategory in possibleCategories %}
<li>
<label>
{{ input(
'checkbox',
'fields[myFieldHandle][]',
possibleCategory.id,
{ checked: possibleCategory.id in relatedCategoryIds }
) }}
{{ possibleCategory.title }}
</label>
{% ifchildren %}
<ul>
{% children %}
</ul>
{% endifchildren %}
</li>
{% endnav %}
</ul>