Stock-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Outstanding, Beginning Balance | shares	220,383
Number of Shares, Granted | shares	3,672,351
Number of Shares, Exercised | shares	(16,370)
Number of Shares, Forfeited | shares	(345,658)
Number of Shares, Outstanding, Ending Balance | shares	3,530,706	220,383
Number of Shares, Exercisable at September 30, 2021 | shares	927,403
Weighted Average Exercise Price, Beginning Balance | $ / shares	$ 0.64
Weighted Average Exercise Price, Granted | $ / shares	6.38
Weighted Average Exercise Price, Exercised | $ / shares	0.88
Weighted Average Exercise Price, Forfeited | $ / shares	5.29
Weighted Average Exercise Price, Ending Balance | $ / shares	6.16	$ 0.64
Weighted Average Exercise Price, Exercisable at September 30, 2021 | $ / shares	$ 4.89
Weighted Average Remaining Contractual Term, Outstanding	9 years 8 months 12 days	9 years 4 months 24 days
Weighted Average Remaining Contractual Term, Granted	9 years 7 months 6 days
Weighted Average Remaining Contractual Term, Exercisable	9 years 7 months 6 days
Aggregate Intrinsic Value, Outstanding | $	$ 34,755	$ 348
Aggregate Intrinsic Value, Exercisable | $	$ 10,304