When ran against your chess data export from Lichess, prints out the dates during which you played no games.

when-no-chess.py

#!/usr/bin/env python3

import re
import datetime

played_chess_on = set()
with open("/Users/johnsullivan/Downloads/lichess_johncs_2021-03-04.pgn") as f:
	for line in f:
		match_obj = re.match(r'^\[Date "([^"]+)"]\s*$', line)
		if match_obj:
			played_chess_on.add(match_obj.group(1))

cur_day = datetime.date.today()
for i in range(365):
	cur_day_str = cur_day.strftime("%Y.%m.%d")
	if cur_day_str not in played_chess_on:
		print(cur_day_str)

	cur_day -= datetime.timedelta(1)