Using Moodle 4.4, while opening a course, I get this error message:
Exception - Call to undefined function shell_exec()

More information about this error
Debug info:
Error code: generalexceptionmessage×Dismiss this notification
Stack trace: * line 175 of /filter/algebra/filter.php: Error thrown

• line 515 of /lib/filterlib.php: call to filter_algebra->filter()
• line 188 of /lib/filterlib.php: call to moodle_text_filter->filter_stage_post_clean()
• line 230 of /lib/filterlib.php: call to filter_manager->apply_filter_chain()
• line 240 of /lib/classes/formatting.php: call to filter_manager->filter_text()
• line 1449 of /lib/weblib.php: call to core\formatting->format_text()
• line 603 of /course/format/tabs/classes/output/renderer.php: call to format_text()
• line 334 of /course/format/tabs/classes/output/renderer.php: call to format_tabs\output\renderer->format_summary_text()
• line 256 of /course/format/tabs/classes/output/renderer.php: call to format_tabs\output\renderer->render_section()
• line 151 of /course/format/tabs/classes/output/renderer.php: call to format_tabs\output\renderer->print_sections()
• line 48 of /course/format/tabs/format.php: call to format_tabs\output\renderer->print_tabs_page()
• line 348 of /course/view.php: call to require()
  I'm still debugging, but I have never seen this in previous versions. When Algebra notation filter is disabled, the course page does open normally.