Octave, 27 bytes

@(x)datestr(x/86400+now,10) 

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How it works

@(x) % Define anonymous function with input x x/86400 % Divide input by 86400, to convert to days now % Current time in days since "January 0, 0000" + % Add datestr( ,10) % Convert to string with format 10, which is year 

Octave / MATLAB, 27 bytes

@(x)datestr(x/86400+now,10) 

Try it online!

How it works

@(x) % Define anonymous function with input x x/86400 % Divide input by 86400, to convert to days now % Current time in days since "January 0, 0000" + % Add datestr( ,10) % Convert to string with format 10, which is year 

Octave, 27 bytes

@(x)datestr(x/86400+now,10) 

Try it online!

Octave, 27 bytes

@(x)datestr(x/86400+now,10) 

Try it online!

How it works

@(x) % Define anonymous function with input x x/86400 % Divide input by 86400, to convert to days now % Current time in days since "January 0, 0000" + % Add datestr( ,10) % Convert to string with format 10, which is year