The use of get_template_part() returns ‘invalid argument’ loading options

You should have a read here. Kaiser wrote a complete article on this on his blog

I quote from that

Although get_template_part is similar to a PHP include or require, you
should not use it to include things like your theme options code,
sidebars registration, custom widgets, etc. The get_template_part
function should only be used to get template parts.

You can go and check out the complete article here

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