The Government will more than double DCMS' budget but the extra funding all but vanishes in 2022.
The 2020 Spending Review has offered hope to struggling arts and cultural organisations but little ongoing support.
Commitments from Chancellor Rishi Sunak that are most likely to benefit the sector include a £4.8bn Levelling Up Fund, match-funding for expiring EU funding programmes, and an extra £2.8bn for DCMS - more than double the department's budget for the 2019/20 financial year and three times the current rate of inflation.
The issue, Institute of Fiscal Studies Director Paul Johnson says, is that while Sunak has increased spending by a "truly astonishing" amount in response to the pandemic, "he has also allocated precisely nothing for Covid-related spending after next year".
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All but £300m of the boost to DCMS' budget vanishes after 2021, bringing the department's allocation down from £5bn next year to £2.4bn in 2022.
And the £20 per week increase to another potentially crucial support for the arts sector at this time - Universal Credit - will be dropped at the end of next year.
IFS called the assumption that increases to spending would not continue beyond 2021 "questionable".
"It seems more likely than not that spending will end up significantly higher than set out today," Johnson said on Wednesday (November 25).
Cultural organisations will have to compete against other local authority spending priorities for a cut of £600m available through the Levelling Up Fund next year.
Sunak said the fund would support, among transport, infrastructure, and high street regeneration projects, more museums, libraries and galleries: "This Government is funding the things that people want and places need."
It aims to "move away from a fragmented landscape with multiple funding streams" to create a cross-departmental fund for English councils to invest in projects of up to £20m, including arts and culture.
The Government will launch the first round of the competition in the new year.
ISM Chief Executive Deboarah Annetts said the Review has "failed to recognise the economic value of the creative industries".
"We are pleased that the Levelling Up Fund covers local arts and culture, but this social infrastructure is too important to be included in the same funding allocation as transport infrastructure."
Theatres Trust called for the fund to support the nation's theatre buildings.
"Our research has identified more than 80 theatre building improvement projects that are currently in development but are at risk due to Covid," Director Jon Morgan said.
"These projects would provide new community facilities with improved access and environmental performance and would benefit from timely government investment."
Creative Industries Federation CEO Caroline Norbury said "urgent clarity" is needed on what will replace Creative Europe.
The UK Shared Prosperity Fund will "at least match reciepts from EU structural funds" of £1.5bn, the Spending Review says. The Government will provide additional funding to support new pilot programmes over the 2021/22 year.
"We look forward to seeing the long-awaited details on the UK Shared Prosperity Fund and urge that government consults with industry as it pilots these new approaches," Norbury said.
"EU funding has been crucial in enabling creative entrepreneurs and organisations to deliver social and economic value, whilst cementing the UK’s position as world-leading."
DCMS' settlement includes £150m for major events including the 2022 Commonwealth Games in Birmingham, celebrations for the Queen’s Jubilee, and Festival UK, often dubbed the 'Festival of Brexit'.