Site with page
https://www.aviso.altimetry.fr/data/products/ocean-indicators-products/mean-sea-level/products-and-images-selection-without-saral-old.html
is now back working, after an absence of a month or two.
To the eye , the reference plot shows something of a curve, top and
bottom of the trace is subatantially above the linear "fit" and middle
is below the straight line. So what sort of curve is the best RMS
least-square fit,ie curves with zero, constant, decreasing or increasing
acceleration?

Firstly using all 1007 datapoints of the Reference plot from 1993 to
2020.404245 , as a partial check on my processing and as a check for
anyone else repeating this.
Linear "fit" , here y is cm as Aviso and x=0 for year 1990.0000 (to
avoid problems if using an exponential or indicial curve-type, but just
the linear here)
y= 0.341193*x -1.607415
R^2= 0.98572
Agreeing with the rounded to 3.41, as mm/year, of the Aviso plot
As explained below , I prefer to start from 2003 and just the Jason
missions.
Ranking of fit by R*R, ie closest to 1 is best curve fit.
x=0 for year 2000.0000 and for the following curves
Linear
y= 0.3751*x + 1.35
R*R=0.972487
SLR to 2100, 38.9cm

Exponential
y=2.20 -4.47675*(1-exp(0.04735*x))
R^2=0.984027
slr to 2100 = 5.05metres

Quadratic
y=2.38 + 0.15843*x + 0.009259*x^2
R^2= 0.98450
slr to 2100= 110.82cm

Indicial (best fit)
y=2.64 + 0.06310*x^(1.55207)
R^R= 0.984715
SLR to 2100 = 82.87cm

History of these results, ranking by R*R, goodness of fit, for best
curve type each time usual the indicial form and decreasing acceleration
, using 2003 to the latest datapoint to avoid the early altimeter
calibration problem and post-Pinatubo recovery SLR flattening and
including the 1993 to 2003 tranche does not actually make much
difference to projections.
Initially melding together the separate J1,J2 and J3 plots and then
since 2019 using the Aviso Reference data as the small GIA component is
getting less and less significant and less and less confidence in the
mission cross-over/overlap data, going in and out of the filters.
SLR to year 2100 using Dec 2017 data of May2017 , J1+J2 only , 56.2cm
data to 25 May 2018 to 2100 , SLR 57.1 cm
data to 02 Aug 2018 to 2100 , SLR 50.5 cm
Update data to 01 Sep 2018, public output 07 Dec 2018
SLR to year 2100 , 49.0 cm
Update data to 01 Oct 2018, public output 18 Jan 2019
SLR to year 2100 , 50.9 cm
Update data to 29 Nov 2018, public output 02 Feb 2019
SLR to year 2100 , 77.4 cm
Update data to 26 June 2019, public output 07 September 2019
SLR to year 2100 , 80.2 cm

Update to 25 July 2019, 02 Nov 2019 public output,
SLR to 2100, 88.2cm

Update 11 January 2020
for data 2003.002659 to 2019.806999,
SLR to 2100 , 88cm

01 Dec 2019 output to the public 15 Feb 2020
SLR to 2100, 117cm (quadratic was the best fit that time, otherwise
indical was 89cm)

624 datapoints from year 2003.002659 to year 2019.9699
output to the public 29 Feb 2020.
SLR to 2100, 88.5cm

640 datapoints 2003.002659 to 2020.404245 website back working on
20 July 2010
SLR to 2100 = 82.9cm

Emlargement of the above and a few images on my page below
--
Global sea level rise to 2100 from curve-fitted existing altimetry data
http://diverse.4mg.com/slr.htm