Installing dependencies fail

[HoneyIsMoney]

to reproduce

git clone https://github.com/gnosis/ido-contracts

cd ido-contracts

yarn

yarn build

error

❯ yarn build
yarn run v1.22.10
warning ../package.json: No license field
$ hardhat compile
An unexpected error occurred:

/Users/x/projects/ido-contracts/src/tasks/initiate_new_auction.ts:64
            .initiateAuction(auctioningToken.address, biddingToken.address, taskArgs.orderCancellationEndDate ?? 0, taskArgs.auctionEndDate ?? now + 360000, sellAmountsInAtoms, minBuyAmountInAtoms, minParticipantsBuyAmount, minFundingThresholdInAtoms, taskArgs.isAtomicClosureAllowed, taskArgs.allowListManager, taskArgs.allowListData);
                                                                                                               ^

SyntaxError: Unexpected token '?'
    at wrapSafe (internal/modules/cjs/loader.js:1054:16)
    at Module._compile (internal/modules/cjs/loader.js:1102:27)
    at Module.m._compile (/Users/x/projects/ido-contracts/node_modules/ts-node/src/index.ts:1056:23)
    at Module._extensions..js (internal/modules/cjs/loader.js:1158:10)
    at Object.require.extensions.<computed> [as .ts] (/Users/x/projects/ido-contracts/node_modules/ts-node/src/index.ts:1059:12)
    at Module.load (internal/modules/cjs/loader.js:986:32)
    at Function.Module._load (internal/modules/cjs/loader.js:879:14)
    at Module.require (internal/modules/cjs/loader.js:1026:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at Object.<anonymous> (/Users/x/projects/ido-contracts/hardhat.config.ts:11:1)
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

environment

macOS Catalina: 10.15.7 (19H524)