try my variant:
<?php if (!is_user_logged_in()) : ?>
<form action="<?=get_home_url(); ?>myaccount" method="POST">
<input type="submit" value="<?php _e('Hello, Client! Click to sign in:', 'theme'); ?>">
</form>
<?php else: ?>
<a href="<?=get_home_url();?>myaccount"><?php _e('Hello ', 'theme'); echo wp_get_current_user()->user_login;?></a>
<a href="<?=wp_logout_url(esc_url( 'https://'. $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'] ));?>myaccount">Logout</a>
<?php endif; ?>