Misti / Ethel
These are the requirements for a Third Country citizen which UK citizen will be in the event of a no-deal Brexit. To me that doesn't look very different to what you describe is required for Americans.
Even if you manage to bag yourself a Frenchman, it is four years before the French government will recognise the marriage as a valid reason to grant residency.
Foreign nationals wishing to reside in France for more than 90 days, whether for personal reasons (family reunion, retirement, etc.) or professional reasons (starting up a business, taking up paid employment, etc.), must submit a long-stay visa application to the French consular authorities in their country of residence.
Find the relevant diplomatic or consular authority
This type of visa allows the holder to live in France for a specified period.
During this validity period, it grants the holder the same rights as the holder of a temporary residence permit or multi-year residence permit. It also allows the holder to apply to the Préfecture in their place of residence for a residence permit so they can stay in France.
The appropriate type of long-stay visa depends on the reason for the stay:
To work or invest in France:
The ‘Posted employee ICT’ visa for intra-company transfers.
The ‘Talent Passport’ visa and its 10 categories, for the purposes of applying for a multi-year Talent Passport residence permit for all planned stays of over 12 months. For all stays of under one year, a VLS-TS is granted.
The ‘working holiday’ visa for eligible young foreign nationals.
To study:
The ‘student’ visa (VLS-TS).
The ‘school-age minor’ visa.
To undertake an internship or training: The visa for ‘interns and young professionals in training’ (VLS-TS).
For tourist, family or personal visits or business travel: The ‘visitor’ visa (VLS-TS).
For family reunification.
Taken from www.welcometofrance.com/en/applying-for-a-long-stay-visa